Am I correct in assuming that this barrel could be screwed onto any short action post64 M70 and function properly with not other modifications? TIA

no the 225 had a different follower and magazine box, i had one of the mod 70's

All of the 225s were made on a long action, so the magazine had to be modified. On a short action, the 225 should fit ok, right?

I think the bolt face may need to be modified, too.