Some rocker arms and other small details where just parkerized but most are nickelled. Maybe the parkerized parts did have some added sealing proceedure done to them. I don't really know but thinks some batches of parts where withdrawn from the line for maybe trouble with the acid bath, rinsing bath or nickel bath solution, electric power supply or conveyor line. You know with a assembly line, the show must go on...

So it is of your prefered choice, black or nickel. Both are genuine original.

I don't know but think the Factory did not introduce cadmium plating until years later.