The 700cc cylinders can use the 750cc piston as an oversize if they need to be bored that far. There are fair amount of interchangeable parts used between the two but the heads, cylinders, crankshaft, and case are different. The valve train, with the exception of the push rods, is all interchangeable. Ignition systems and much of the primary & transmission are interchangeable too. The Galaxy models were the only single carburetor version of the 750 but they had a special manifold to cross over.