In response to the question of what was changed on the model 94s after 1964, I remember that when I was still in high school we went to Spokane. At this time the Crescent sporting goods store still sold firearms, and they had a new model 94 in stock. The thing that stuck out was that the cartridge follower was a piece of stamped steel, no curve to it, just flat, unlike the machined steel found in the older rifles. Even though I was a teenager then the difference really jumped out at me. There were other changes, too, but that's the one that really stood out, as I had a pre-64 at home and was curious to see what new ones looked like.
Jack