I primed mine with epoxy primer. You have it all down to bare metal, why not spray it with something that will likely outlive you?
It lays down nice and sands a lot better than I expected.
Once you get done with the body work, give it another coat to seal in any filler. This can be done one area at a time if you you cannot knock out the cab body work in quick order.
Carl

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