The main difference is the pre-64 was CRF (control round feed) --the post 64 was push feed, but some called it "POS".
Another major difference that some overlook, is the trigger assy. -- The pre-64 trigger and sear were machined from chrome molly steel (winchester proof steel). These are one of the best trigger assys. around. --- The post 64's were made from castings. The sharp edge would round off and they could mis-fire. I had one. Flip the safety off from safe to fire real quick and the rifle would sometimes fire. Got it repaired and got rid of it.
There were of course other differences as the post 64 was a completey redesigned rifle than the pre-64. Winchester hired an out of shop design team that came up with the new rifle. -- Stamp, Press, and Push is what some of the Old Guard called them. Jack O'Connors was a big fan of the pre-64 M70 and was very vocal of his disapproval of the post 64 M70.
Rod