I don't know if any barrel makers who will pre-thread a barrel for the M70 Classic. Push feeds, sure, is just a simple 1x16 same as Ruger. But the Classic had a coned breech and the extractor cut. Even if you were to look at the companies who will put the barrel on for you, notice most charge extra for CRF winchester rifles, because of that.
I might be leary of a re-bore in this situation, if it's a known bad barrel. Then again it might turn it into a great shooter. Might have to shorten the barrel a smidge to get to the .580-.600 diameter range though