[MP&C]

I've made special purpose dollies and dies before, what comes to mind for this (if I were trying to straighten the crease) would be to cut a piece of 12 gauge or so flat sheet into about a 12" long piece, (height...at least 6" or so for vise clamping) and cut the top into a gentle, sweeping curve. You want it close to matching what is on the underneath of the good side, but enough radius that the ends don't touch the bottom of the hood. You don't want too much radius that it tries to push a high spot in the middle. So find the happy medium.... Then I would tack weld a 1/4" steel rod to the top, to eliminate any sharp edges from pushing into your sheet metal. Now clamp in a vise, position hood over top of your fixture, and gently push downward to bring the crease up. Use extreme patience, get some help to hold the hood in the air, and use slight pressure where needed to persuade the low side upwards. SLOWLY, I would add, better to sneak up on the end goal than going past it at 90 mph and having to bring it back down again. If you don't have a vise and a friend, then take the hood off and lay in the grass, use the dolly fixture as a punch with a dead blow hammer. Light taps until you see how the metal responds, again, so you can sneak up on the result you seek.