Paid to restore a car.... Questions.
Another thing I know a few guys around me do is make the owner pay as they go or the work stops. You work 40 hours, you bill it, he pays or it gets put in the corner. Seems to be a decent way to prevent you from getting it done and the owner not having the money or complaining and trying to get it for cheaper once it's done. Make sure he knows up front the reality of paint and body work and that he doesn't think this is a "good buddy" deal expecting a show car for the price of a Maaco special.
Is the owner mechanical at all? Can he do any of the disassembly himself to save the costs of you doing it? If he wants to do it right then he should consider having someone blasting it instead of paying you to strip it. Then you can see everything and give him a lot better estimate of what's there and what needs to be done. That old paint can hide a lot and it would probably be cheaper in the long run.