GM had no real way to selectively paint the basic engine.....air cleaner is
a different story. Look at the gaskets.....to see if the engine has been apart.

For the engines with aluminum valve covers, I think they layed a mask (perhaps just a steel cover) on the engine during painting. For aluminum intakes, they had a cardboard valley cover to mask

Sounds like a dealer did an engine for the bicentennial....'76. They did some montes or monzas with a really ugly red/white/blue scheme back then.....looked like an Arkansas Clap Doctor's car.

mike in tucson