I also thought about the possibility the owners may want to move into more serious type car down the track. A minimum buyback/trade in price could be offered, maintainance/damage clauses would need apply. With a trade in there could be an oppurtunity for the "builders" of the cars also knocking out restored classics.
Dunno about an ideas man Justang, I know my head is full of crap, dont know if much is usefull though. Depends on who you ask:w