diff --git a/src/openrct2/FileClassifier.cpp b/src/openrct2/FileClassifier.cpp
index c865ba018d..f9e4547228 100644
--- a/src/openrct2/FileClassifier.cpp
+++ b/src/openrct2/FileClassifier.cpp
@@ -15,6 +15,7 @@
 #include "core/String.hpp"
 #include "park/ParkFile.h"
 #include "rct12/SawyerChunkReader.h"
+#include "rct2/RCT2.h"
 #include "scenario/Scenario.h"
 #include "util/SawyerCoding.h"
 
diff --git a/src/openrct2/management/Research.cpp b/src/openrct2/management/Research.cpp
index 98a8c06e09..0f13a4fbcb 100644
--- a/src/openrct2/management/Research.cpp
+++ b/src/openrct2/management/Research.cpp
@@ -23,7 +23,6 @@
 #include "../localisation/StringIds.h"
 #include "../object/ObjectList.h"
 #include "../object/RideObject.h"
-#include "../rct1/RCT1.h"
 #include "../ride/Ride.h"
 #include "../ride/RideData.h"
 #include "../ride/RideEntry.h"
@@ -68,35 +67,6 @@ static bool _researchedSceneryItems[SCENERY_TYPE_COUNT][UINT16_MAX];
 
 bool gSilentResearch = false;
 
-// TODO: MOVE TO S4/6 IMPORT
-ResearchItem::ResearchItem(const RCT12ResearchItem& oldResearchItem)
-{
-    if (oldResearchItem.IsInventedEndMarker() || oldResearchItem.IsUninventedEndMarker() || oldResearchItem.IsRandomEndMarker())
-    {
-        rawValue = 0;
-        flags = 0;
-        category = ResearchCategory::Transport;
-        SetNull();
-    }
-    else
-    {
-        type = Research::EntryType{ oldResearchItem.type };
-        entryIndex = RCTEntryIndexToOpenRCT2EntryIndex(oldResearchItem.entryIndex);
-        flags = oldResearchItem.flags;
-        category = static_cast<ResearchCategory>(oldResearchItem.category);
-        if (type == Research::EntryType::Ride)
-        {
-            auto* rideEntry = get_ride_entry(entryIndex);
-            baseRideType = rideEntry != nullptr ? RCT2::RCT2RideTypeToOpenRCT2RideType(oldResearchItem.baseRideType, rideEntry)
-                                                : oldResearchItem.baseRideType;
-        }
-        else
-        {
-            baseRideType = 0;
-        }
-    }
-}
-
 /**
  *
  *  rct2: 0x006671AD, part of 0x00667132
diff --git a/src/openrct2/management/Research.h b/src/openrct2/management/Research.h
index def062b443..cbfa059335 100644
--- a/src/openrct2/management/Research.h
+++ b/src/openrct2/management/Research.h
@@ -10,8 +10,8 @@
 #pragma once
 
 #include "../common.h"
+#include "../object/Object.h"
 #include "../object/ObjectLimits.h"
-#include "../rct2/RCT2.h"
 #include "../util/Util.h"
 
 #include <optional>
@@ -87,35 +87,9 @@ struct ResearchItem
     {
     }
 
-    RCT12ResearchItem ToRCT12ResearchItem() const
-    {
-        RCT12ResearchItem retItem = {};
-        if (IsNull())
-        {
-            retItem.rawValue = RCT12_RESEARCHED_ITEMS_SEPARATOR;
-        }
-        else
-        {
-            retItem.entryIndex = OpenRCT2EntryIndexToRCTEntryIndex(entryIndex);
-            retItem.baseRideType = RCT2::OpenRCT2RideTypeToRCT2RideType(baseRideType);
-            retItem.type = static_cast<uint8_t>(type);
-            retItem.flags = (flags & ~RESEARCH_ENTRY_FLAG_FIRST_OF_TYPE);
-            retItem.category = EnumValue(category);
-        }
-
-        return retItem;
-    }
-
-    ResearchItem(const RCT12ResearchItem& oldResearchItem);
-
     bool operator==(const ResearchItem& rhs) const;
 };
 
-// Only used to mark as null nowadays. Deprecated. TODO: remove.
-#define RESEARCH_ITEM_NULL 0xFFFFFFFF
-
-#define MAX_RESEARCH_ITEMS 500
-
 enum
 {
     RESEARCH_FUNDING_NONE,
diff --git a/src/openrct2/rct12/RCT12.cpp b/src/openrct2/rct12/RCT12.cpp
index 0fe0c50c21..fab801189d 100644
--- a/src/openrct2/rct12/RCT12.cpp
+++ b/src/openrct2/rct12/RCT12.cpp
@@ -13,6 +13,8 @@
 #include "../localisation/Formatting.h"
 #include "../localisation/Localisation.h"
 #include "../object/ObjectList.h"
+#include "../rct2/RCT2.h"
+#include "../ride/Ride.h"
 #include "../ride/Track.h"
 #include "../scenario/Scenario.h"
 #include "../world/Banner.h"
@@ -911,3 +913,34 @@ money32 OpenRCT2CompletedCompanyValueToRCT12(money64 origValue)
 
     return ToMoney32(origValue);
 }
+
+ResearchItem RCT12ResearchItem::ToResearchItem() const
+{
+    auto newResearchItem = ResearchItem();
+    if (IsInventedEndMarker() || IsUninventedEndMarker() || IsRandomEndMarker())
+    {
+        newResearchItem.rawValue = 0;
+        newResearchItem.flags = 0;
+        newResearchItem.category = ResearchCategory::Transport;
+        newResearchItem.SetNull();
+    }
+    else
+    {
+        newResearchItem.type = Research::EntryType{ type };
+        newResearchItem.entryIndex = RCTEntryIndexToOpenRCT2EntryIndex(entryIndex);
+        newResearchItem.flags = flags;
+        newResearchItem.category = static_cast<ResearchCategory>(category);
+        if (newResearchItem.type == Research::EntryType::Ride)
+        {
+            auto* rideEntry = get_ride_entry(newResearchItem.entryIndex);
+            newResearchItem.baseRideType = rideEntry != nullptr ? RCT2::RCT2RideTypeToOpenRCT2RideType(baseRideType, rideEntry)
+                                                                : baseRideType;
+        }
+        else
+        {
+            newResearchItem.baseRideType = 0;
+        }
+    }
+
+    return newResearchItem;
+}
diff --git a/src/openrct2/rct12/RCT12.h b/src/openrct2/rct12/RCT12.h
index b0ea2b0b62..30e6e76c02 100644
--- a/src/openrct2/rct12/RCT12.h
+++ b/src/openrct2/rct12/RCT12.h
@@ -12,6 +12,7 @@
 // Structures shared between both RCT1 and RCT2.
 
 #include "../common.h"
+#include "../management/Research.h"
 #include "../object/Object.h"
 #include "../ride/RideTypes.h"
 #include "../world/tile_element/TileElementType.h"
@@ -838,6 +839,8 @@ struct RCT12ResearchItem
     bool IsInventedEndMarker() const;
     bool IsRandomEndMarker() const;
     bool IsUninventedEndMarker() const;
+
+    ResearchItem ToResearchItem() const;
 };
 assert_struct_size(RCT12ResearchItem, 5);
 
diff --git a/src/openrct2/rct2/S6Importer.cpp b/src/openrct2/rct2/S6Importer.cpp
index 4fbf1bbbb9..29e695e7f3 100644
--- a/src/openrct2/rct2/S6Importer.cpp
+++ b/src/openrct2/rct2/S6Importer.cpp
@@ -299,13 +299,14 @@ namespace RCT2
             gResearchPriorities = _s6.active_research_types;
             gResearchProgressStage = _s6.research_progress_stage;
             if (_s6.last_researched_item_subject != RCT12_RESEARCHED_ITEMS_SEPARATOR)
-                gResearchLastItem = ResearchItem(
-                    RCT12ResearchItem{ _s6.last_researched_item_subject, EnumValue(ResearchCategory::Transport) });
+                gResearchLastItem = RCT12ResearchItem{ _s6.last_researched_item_subject,
+                                                       EnumValue(ResearchCategory::Transport) }
+                                        .ToResearchItem();
             else
                 gResearchLastItem = std::nullopt;
             // pad_01357CF8
             if (_s6.next_research_item != RCT12_RESEARCHED_ITEMS_SEPARATOR)
-                gResearchNextItem = ResearchItem(RCT12ResearchItem{ _s6.next_research_item, _s6.next_research_category });
+                gResearchNextItem = RCT12ResearchItem{ _s6.next_research_item, _s6.next_research_category }.ToResearchItem();
             else
                 gResearchNextItem = std::nullopt;
 
@@ -1003,9 +1004,9 @@ namespace RCT2
                 }
 
                 if (invented)
-                    gResearchItemsInvented.emplace_back(researchItem);
+                    gResearchItemsInvented.emplace_back(researchItem.ToResearchItem());
                 else
-                    gResearchItemsUninvented.emplace_back(researchItem);
+                    gResearchItemsUninvented.emplace_back(researchItem.ToResearchItem());
             }
         }