I've used the Harland Sharp, not on a real hi-performance FE, but they did work quite well, never broke anything anyway....

Depending on the performance level you're shooting for, might also want to take a look at the Blue Thunder heads. They have some rockers that are for their heads, IMO the best setup on the market.... Another good source is good ol' Barry at Survival Motorsports, some really first rate FE goodies and probably one of the best FE shops around.....