I want to repaint my HO valve covers and am curious as to what the original color was. Were these a dark gray or a silver when new? Also will paint from auto parts stores hold up? ( hi-temp paint ) Thanks, Ray.
The HO aluminum valve covers were bare metal. I painted the ones on my old T-Bird Ford Red (because the car had a red & white theme) and the paint held up very well. I sanded them to remove the rough as-cast finish, and the red paint went on and stayed nice and shiny. I'd imagine any aluminum-look high heat or engine paint would work for you if you want the factory look
Later HO valve covers (90ish and up) were painted some sort of gray shade. The earlier ones weren't painted but the later ones were.
If it helps, these pics are of a 1990 asc/McLaren Mustang that is all original and hasn't been touched.

Looks like some kind or gray. Same as the upper intake.
I know the upper intake and valve covers on my 91 Mark VII are painted a light gray and not as cast.