The assembled engines were not painted as normal cast iron engines but certain steel components were painted. The ZL1 engine assembly manual shows that "black engine enam" was to be used to paint the "oil pan, air inj brkt, distr clamp, frt cover, clutch fork (exposed part), torsional damper, lifting hook, exh manif, clutch hsg cover".
Normal manufacturing processing would dictate these parts were painted prior to assembly. Automotive fasteners are coated and do not need to be painted. http://www.camaros.org/copo.shtml#engine