I don't know if the fittings had red lead primer or another coating on them before installation on the assembly line. I agree with you the fittings and the bypass hose were installed before engine paint.
Over the years I have bought some NOS pieces but they have a more shiny look compare to the assembly line parts I was fortunate to be given in 2009. They looks more steel gray.
The repops as you see on the picktures has been given a finish, like silver zink. Factory parts did'nt have anything, but I'm not sure if they were shot in primer!