Changing color of frame

[ford35lh]

I bought a restored 1 1/2T chassis ,complete except for the engine.
The color is silver gray and I want to paint it black.
It appears that the metal was blasted as the pitting is not too deep and very clean.
I tried rubbing a remote area of the paint with laquer thinner,brake fluid and carb cleaner.
It was untouched.
Any suggestions how to overcoat this paint ???