As Bill stated, taking apart the grill for painting would seem to be the best way to get a good result.
If you are interested in original color-names, in 1953 the radiator grill-bars (inner surfaces) and hub caps were painted Thistle Gray.
Bumper facing were gray (most likely Anvil Gray).
Argent Silver was the inner-bar color on painted grills on 1954 trucks that had the Commercial Red exterior color. This was supposedly used because the Commercial Red bled through the Thistle Gray. Argent Silver might also have been used on Red trucks' inner grills in 1953.
