Grey Phosphate is the correct finish. I've used Eastwood's cast iron powder for great results. On another car I used weld-thru primer but that produced a too light color.
I had my hood hinges repaired and powder coated by Hoodhingerepair.com in Virginia. The work fantastic and the powder coating looks great. I had them done in satin black.
Here's a pic of the hinge I powder coated with the Eastwood cast iron. In the center is a clutch linkage bracket with the original grey phosphate. Hardly a perfect match but I do like the results.
Save yourself some money and spray with SlipPlate. Also works excellent of exhaust manifolds keeping them looking like new. https://www.amazon.com/Slip-Plate-P...ip+plate+graphite+spray&qid=1573490100&sr=8-4