Well, Winchester Model 70s, aside from being manufactured in two different action/ receiver lengths, are also available in two diferent bolt styles, the push-feed and the controlled-round feed. The main difference is the type of extractor used. The controlled -round model uses a flat spring extractor which looks like a flat bar running along the right side of the bolt. It picks up the cartridge from the magazine as you begin to push the bolt forward, and thus allows you to extract that cartridge before it is completely chambered, should it begin to jam up for whatever reason. The push-feed models use a round bolt with a much smaller extractor at the front end, which doesn't engage the cartridge rim until it snaps over it, after the cartridge is fully chambered. The controlled -round models are generally considered a bit more reliable and are preferred by hunters of dangerous game. They will chamber a cartridge when the gun is held upside-down, should that ever become important to you.
The push-feed receivers are a little more symmetrical, and are thus considered by target shooters to be a little more conducive to fine accuracy. ( Vibration patterns, barrel harmonics, etc.)
My previous post simply raised the question of whether each of those styles required different bases, because of different top contours or not. I really don't know.
Edited by RONK