I used to build some sneaky-Pete cheater engines for the claimer-class cars. Since the 64CC camel-hump heads were illegal for that class, we would take the 76 CC low compression heads and do a .100" angle mill from the spark plug side of the head where the majority of the combustion chamber volume was located. The result was a 60 CC head with a 76 CC casting number. A set of 1.6" exhaust valves and some pocket porting resulted in an engine that would outrun one with the camel-hump heads, and the tech inspectors had to do a full teardown to catch us. Like Smokey Yunick used to say, "It's only cheatin' if you get caught!"
Jerry