I painted a set of Harley cases years back with red oxide rust-oleum, Harley motors are dry sump and have very little room in the crankcase for excess oil (Big HP Loss). The oil has to get to the bottom of the crankcase quick to be picked up by the wheels where it is scraped off into a oil return troff and is pumped back to the tank. As far as that head I think someone painted it for oil drain back, or display, I lean more towards oil drain back.