Smoking 440

If it smokes under acceleration and is pressurizing the crankcase its probably blow-by from bad rings. If it smoked more at start up and idle that would be valve guides/seals.

A compression test would tell you how bad things are, but a leak down test would be better for pinpointing the issue.

As far as the "rebuilt" thing, who knows. Could have been rebuilt poorly/wrong, or he could have just been telling you what you wanted to hear. Until you break it open, its pretty hard to tell. If I bought a lot of used engines I'd invest in a borescope, they really aren't that much money anymore. Heck I've thought about getting one just for diagnostics on the engines I have. But even that won't show you something like the rings installed upside down.