I would take it to a body shop and see how much they would charge to either knock it out or replace the panel, might be easier than doing it yourself. Your Stang reminds me of the '84 I used to have it was a V6.

 

Wow $1000 to change the Quarter.I could do it for $500-600.But i don't have much overhead.Hes pretty accurate with the paint price $2000-2500