They were only available on the high performance solid lifter rectangular intake port HiPerf engines. The Corvette differed from passenger cars by having a sloping drivers side cover to clear the power brake booster on install or removal to adjust valves. All Pass engines received painted covers. Also the HiPerf engine had grooved rocker balls and long slot (stamped H) rocker arms while the Pass cars had smooth rocker balls.
Chromed or painted all BBC covers had oil drippers under the cover up until 1972 when they went away on Pass engines and a year later on HiPerf engines. You really want a reproduction cover with oil drippers with a modern cam as they are as aggressive as the solid lifter cams of the early sixties.
BBC also all used to have 7/16th inch diameter push rods up until 1972, after that they were all 3/8th inch in diameter like the earlier SBC used (after 1972 the SBC went to 5/16th inch diameter push rods as smog cams entered the production line). To use a 7/16th inch push rod on a modern motor you have to replace the guide plate for the push rod as well.
The only other thing to add is a painted cover will resist oil leaks better than a chromed one as the cork gaskets won't seal against the polished chrome plating. That is why the factory went to die cast aluminum valve covers with the Gen V and Gen IV engines. They used an O-ring to seal instead of a cork gasket.
Since only a "real" SS Camaro, Chevelle, or Nova with a HiPerf BBC under the hood had chrome valve covers the aftermarket (Cal Custom, M/T, Edelbrock, or Chevrolet's service department selling Corvette or Chevrolet finned die cast covers where as common as painted covers back in the sixties. It was like mag wheels and Hurst shifters, everybody couldn't wait to upgrade their ride from stock with aftermarket parts found in car mags of the sixties.