As painful as that damage looks, a good body man can pull it, hammer & dolly it, and get it back in shape without cutting off the entire quarter. If the quarter panel is in otherwise ok shape, I suggest trying to save it.
If you have the time and interest, consider looking at an adult education program through the local community college in your area to see about a vocational education introductory course on automotive body and paint. It might actually be a good thing to have those skills sets as you play with these old rigs.
*67 Vintage Burgundy 390GTA with most of the bells and whistles*