I quit the roller idea and used a canvas bank bag filled with lead shot. I sanded and rounded the heads on an old red/green rubber head hammer, sanded an old beat up body dolly smooth, also a cheap body hammer and a small ball peen. I made a couple dents in a single cut fender totally disappear and straightened another one bent near the rear bottom. There's a scratch where the big dent was, if I had it re-chromed it would be beautiful.
Now I have confidence to try some nicer parts. Thousands of tiny taps and piles of patience. I found it relaxing because I considered the part worthless when I began.