71's seem very expensive and costly to restore also. Just as bad as 70's. But, if you are going to put all the work into a car, I think it should be one you love. Hold out for the one you really want and get one as complete as possible.
Other differences between barracuda and cuda are suspension differences for handling and safety in big block cars. If you go with a big block you need to install larger torsion bars, stiffer springs and front and rear torque boxes that stiffen the body front and rear. Otherwise you may crack your bondo when your body twists. Or even tear your rear end out. ouch;D