I just acquired an "improved .220" barrel, and am basically unfamiliar with varmint calibers. Is this different from the .220 swift? This is a 1960's barrel...

Yes, definitely if it is a 60's unit. It certainly won't be a SAAMI Swift. What's the throat look like? You might want to have it set back and rethreaded, and re-reamed with a more up-to-date Swift Improved reamer.

Entrance half of barrel was badly copper-coated - once I got it cleaned, you can see a tapering trace of lands tapering up from nothing at the end of the chamber to decent lands 3-4 inches back. My local smith says that I can shoot standard .220 Swift in it, and it will fire-form to the existing chamber, if I care to reload those. He han't seen the cleaned-out barrel yet to pass judgement... But according to Ackley, some of the wildcats had tapering lands for several inches - I am not sure whether I am looking as severe wear or the way it was made from day one... I have bought a 1940s Winchester model 70 30-06 that I plan to have the smith mount the .220 on...