I assume you are talking about a 216 cu-in straight 6? No roller rockers or lifters are made for the 216-235-261 engine family. There were some "Baker hi-lift" rocker arms made in the '50s, but good luck finding a set. But by the time you got to the RPM range where they'd make a differance, pieces of the motor would be flying through the fenders. The '40s era chevy engines will grenade if revved past 3500 RPM on a regular basis.

The 216 is a "splash-oiled" system that uses dippers and nozzles to spray oil at the big end of the conn rods, as there are no oil passages drilled in the crank. This combined with only 4 main bearings, is not the hot ticket for power.

chip

Preaching the Hot Rod Gospel according to the 4-stroke apostles:

Suck, Squish, Fire and Fumes