Paul, I found a pair of ball bearings on
AMAZON and welded a nut on one to be able to screw it on to a slide hammer. I used that as a dolly inside the bed side roll to remove the flat spots on it. I had to grind off a bit from each side of the ball so there was a spot to hammer down with the full diameter of the ball under the low spot. It actually worked pretty well. I don't recall what the diameter was, but it was a snug fit in the bed roll. I'd have to go dig it out of the garage to measure it.
{on edit} according to the notes
here the ball was 1-1/2 inch diameter.