Winchester's models 1886 and 71 lever actions are nearly mechanically identical. Their loading gate assemblies are different. The 1886 has a multipart assembly affixed to its receiver by a screw. The 71 has a one-piece loading gate, (resetting) spring being incorporated into its gate. This piece is also affixed to its receiver by a screw.

Since affixing screws are in the same location and doing the same function, are the loading gate assemblies interchangeable? If the assemblies are int interchangeable, can either receiver accept both - that is one of the receivers can accept both?

Someone with a lot more technical knowledge that I will probably be along soon. But my understanding is the actions are not nearly identical. The 71 was improved by changing the angle of the locking bars to the bolt requiring I think not just a few minor changes,also, it has a pistol grip stock and curved lever which requires a different tang. My guess is, the loading gates would not interchange as if they could, they probably would have used the same part.