I am in the same boat trying to decide if I should invest the money upgrading my stockers or buy a set of aftermarket heads. I called and talked to 440 Source about thier Stealth heads on a 383 and they did advice me that the valves could interfere with the cylinder walls on a std. bore 383. They said if the motor was .030 over it should be no problem and if the motor was std. a very small amount of clearancing could be required. Doesn't seem like a big deal either way but I did want to throw it out there.