Help with plating color
 

I am rebuilding my motor and wanted to know if I should plate the case through bolts and acorn nuts. If so what should I replace with?

Clear cad
Yellow cad
Yellow zinc

Does anyone know what they were originally plated with?

Yellow zinc.

The case the ought bolts on yellow zinc as well?

Yes,...ALL of the engine hardware.

Wasn't yellow cadmium used originally up through 70-80's? Most yellow nuts/bolts are zinc today since cad has been outlawed as a heavy metal pollutant. Cad is much more corrosion resistant however and is still used for military applications for that reason.

FYI I clearcoat my nuts/bolts with Nylac from Eastwood which dries fast and invisibly. Underbody nuts/bolts I spray with a yellow wax which has a tack and attracts dust but protects and seals.