you wont believe this but grab a old 350 harmonic balancer and lay the cap on your bench in a smooth spot and start working the balancer back and forth on the ding it will push right out and the balancer has just the right edge on it and the weight of it really helps make the work pretty easy, the trick is to hold the cap at a angle and also work the balancer so it is pushing firmly on the ding and the bench with no gap between the cap and the bench or you will make a outwards ding! Yikes! keep flipping it over and look where your low spot is, you did some body work so I know you will see what I am talking about, gently wet sand the outside where the blem was and polish her back up...
Bud.