For a good cruiser with decent power, you will at least be honing the block and replacing the rings, right? The '67 motor will offer the most compression of the 3. The motor home mill likely has LESS than 7.8 to one squeeze. Certainly a durable mill, but waaaay low on compression with pistons .120 down the hole. The '67 motor will likely have near 10 to one and with a decent cam, can run strong on mid grade fuel. With new rings, you ARE going to get a valve job, right? It makes sense to install new springs as well. 44 year old valvesprings on a higher lift new cam..... not good.