85 GT 225,000 miles and needs help.

[DRASTiK]

well as far as how big of a cam can you go, there really isn't a straight answer. Lift isn't the only thing you have to look for in this situation. Some cams with different LSA, duration, etc will have different clearances. For example, one cam with .544 lift might clear, but another cam with .525 lift might not. All of the factors (kind of pistons, how they're flycut, type of valves in heads, and all the cam specs) have to come into play. Not just lift. Sorry, I know this isn't the answer you wanted. If you find people with stock bottom ends (assuming that's what you have because of the questionable rebuild), and stock heads, you could find out what they're running.
Dave