I would degrease it, pressure wash it, weld the rivet head, treat it with Ospho, pressure wash it again to remove the Ospho byproduct residue (white dusty material), then paint with Rustoleum Rusty Metal Primer, then finish with Rustoleum gloss black. This process has worked very well for me and is less expensive and less work than any other method.
Carl

1952 5-window - return to "as built" condition | 1950 3100 with a 235 and a T-5 transmission