Open chambers, Oval ports. Used on a variety of 396-454 apps. Larger valves and some bowl work will be okay for a street motor or a boat. save the rods and crank. Forged crank and the rods are durable stuff. Just don't anticipate going huge HP and TQ numbers. I have one left that can be punched to 4.250 bore and it gives me the opportunity to go longer rods, etc. Good enough stuff to have on hand to build a reliable budget motor with some other good components later.