The GA does need certain bulkheads in place, e.g. the aft cuddy and aft pilot house bulkheads, but there are ways to work around that. The bigger issues are where the CG ends up (must be in the proper fore/aft envelope) and total weight of the boat. Too light and you risk certain instabilities, e.g. chine walking and possible porpoising. That said, building something like a cuddy plus a steering station, and having larger than average fuel tanks in the boat might make up the difference. Hmm....
Brian