That is one fine hotrod you got yourself there !!!!!!!!!

I would get some white spray paint and just lightly fog a coat over the body ( called a GUIDE COAT ) then get a long sanding board and block sand it with 180 or 220 grit , and see all your highs and lows . Some areas may only take a skim coat to get it straight , and other areas may require some bigger attention , but the block sanding will give you a good visual on the work involved to get it right !

Its easier to work bondo if you can hammer and dolly the dents and get the metal as straight as you can ,then to try and fill .

With it having the DP on it you can ruff it up ( the block sanding will be sufficient ) and put your filler over it , as this is how PPG recommends a good repair as the DP is an excellent ground coat for repairs !

I use only 80 grit to sand my filler & then just before I have it where I want it I then go to 180 grit for the final cutting ( This will also help on filling with primer as it doesnt take as much to fill the deep scratches ) , as I can usually spread the filler smooth and not have to cut it with any thing courser .
A cheese grater will cut fast so be sure to use little pressure to shape as you dont want to cut it all off . keep it a tad high & use your blocks & 80 to get it straight .
Hope this helps