The trailing edge of my 147 fenders looked about like that. Stand them up on a 2x4 and prop the tops against a wall or something. Adjust the angle until the back slope of the fender edges lays flat on the 2x4. Get a ball peen or smooth head hammer and pound the waves out. The ground and 2x4 gives a great surface to work against. Light taps, work up and down the trailing edge. Mine came out very straight.
Check the restoration link below, at 1:35 there is a short clip of me doing this:
https://www.youtube.com/watch?v=_FhmC8Mk9Lw