Pre 64's had their good years and bad years. The design was overall an excellent design, not so good on gas handling, but it was a slick and reliable action. It made an excellent target rifle due to its easy and smooth bolt movement and the flat bottomed rigid receiver. Had the best over ride trigger ever put on a commercial rifle.
From what I have seen the pre WWII rifles had the best fit and finish. However quality went down the tubes in the 50's. Winchester machines were antiquated, and their manufacturing processes, well they would be an example of a “bad” factory in a LEAN manufacturing class.
A shooting bud of mine is a pre 64 collector. He claims Winchester lost money on every pre 64 they were producing prior to the end of production. His first pre 64, purchased new in the 50’s, was defective. I forget the fault, either it would not feed rounds, or would not reliably fire rounds. Like I said, the vaunted pre 64 had its bad years.
The actual push feed was not a bad design either. It did drop manufacturing costs and retained a number of the good pre 64 features. When the M70’s and M700’s ruled the Highpower match rifle categories, the post 64 was extensively used and found to be a reliable mechanism. The extractor was the item most likely to wear out. The rest of the rifle rarely broke parts.
An excellent design analysis of the actions is to be found in Stuart Otteson’s Book “The Bolt Action”.
If you can get a push feed M70 in good condition at a good price, go for it. The action is slick, the action as rigid and stiff as it ever was, the safety easy to use, and the trigger is still the best override trigger ever put on a commercial action.