I have a number of pre 64's and they are all a mixed bag. Featherweight barrels are not exactly tack drivers. The collector from whom I have purchased most of my pre 64's, he got a factory new pre 64, in the 50's, and had malfunctions.
The primary problems with the original pre 64's was manufacturing. Based on the reading I have done, Winchester wore out its tooling during WW2 and kept on using the same old machines instead of replacing them. Somewhere I have a picture of the Winchester custom shop, it has to be around the 80's, and leather belts are visible in the picture. These leather belts go from shafts in the ceiling down and around pulley's on machine tools on the ground. This is a very old, and unsafe, way to power machine tools. The machines must have dated prior to WW2. FN did a plant tour, and the trip report is in the book "FAL". What the trip report shows is an complex, confusing, process flow. Process flows that are illogical and confusing create a lot of bad parts.
I am of the opinion that the pre 64 M70 is a good action. There are features I like, particularly the stiff center section, easy bedding, easy bolt lift, fast firing pin fall. I like the three position safety and really like being able to remove the firing pin from the bolt without special tools. Bolt manipulation on a M70 is slick and smooth. The M70 over ride trigger was the best ever on a hunting rifle, though I prefer the two stage military trigger for safety and function. Over ride triggers don't have enough sear engagement to make me feel safe, but they can be tuned to incredible light releases. Anschutz triggers are over ride triggers and they are incredible target triggers.
The cone breech must have been copied from the M1903 and it is inferior to almost all other breeches in protecting the shooter from gas release. It really is awful. I recommend reading Ottesen's book on Bolt Actions for a comparison of actions, and comparisons of case head protrusion. The cone breech leaves a lot of case head hanging out of the chamber. I am of the opinion that case head protrusion is the better metric to compare when discussing action strength. Actions that provide more case head support are "stronger" than those that provide less, because the case is the weakest link in the system.
I think the M98 Mauser action is the best overall action ever built, but it was even more expensive to make than the M70. I am glad the M70 action is still around, even though the pre 64 is not. I have push feed, controlled round feed, and pre 64's. They all go bang and shoot reliably. They shoot accurately if they have a good barrel and are properly bedded.