I think Mavrovic would have some chance against the old Foreman and could win with some hard-fought SD...
Foreman by close UD, especially if it's the 1991-1993 version. If the more mobile, quicker Lewis wasn't able to KO Mavrovic I don't see how Foreman would have. At the same time, Mavrovic didn't have the firepower to trouble Big George, but then again Schulz was able to go toe-to-toe with him and unofficially won (against the even slower 1995 version).