link_objdata_same_models.py

import bpy

mesh_objs = [obj for obj in bpy.context.scene.objects if obj.type == 'MESH']

print('Found ' + str(len(mesh_objs)) + ' mesh objects')
print('Grouping unique mesh data...')

# Create a dictionary to store objects with matching mesh data
mesh_dict = {}

# Iterate through all mesh objects and group them by mesh data
for obj in mesh_objs:
    mesh_data = obj.data
    verts = [v.co for v in mesh_data.vertices]

    # skip planes (probably decals)
    if len(verts) <= 4:
        continue

    verts_key = tuple([(round(v.x, 4), round(v.y, 4), round(v.z, 4)) for v in verts])
    poly_key = tuple([(f.vertices[0], f.vertices[1], f.vertices[2]) for f in mesh_data.polygons])
    mesh_key = (len(verts), verts_key, poly_key)
    if mesh_key not in mesh_dict:
        mesh_dict[mesh_key] = []
    mesh_dict[mesh_key].append(obj)

print(f'Found {len(mesh_dict)} unique mesh data blocks')

already_linked = 0
total_linked = 0

# Link object data for objects with matching mesh data
for key, objs in mesh_dict.items():
    if len(objs) > 1:
        for i in range(len(objs) - 1):
            if objs[i+1].data == objs[0].data:
                already_linked += 1
                continue

            objs[i+1].data = objs[0].data
            print('Linked ' + objs[0].name + ' with ' + objs[i+1].name)
            total_linked += 1

print(f'Successfully linked {total_linked} objects')

if already_linked > 0:
    print(f'Info: {already_linked} objects were already linked')