I dont' have the answer for you, but I am actually going the other way, wanting the indentation on my 75 so I can mount 240z bumpers. I was thinking that I could still mount the larger bumper on the indented quarters if I wanted to. Do you know if this is a problem?
Have a 76 and have purchased rear quarter panels from Chuck at Classic parts and restoration and have already welded them in and they fit perfectlly. 100 beans per side. He also has for 240 and 260. He is a little slow to respond but am completly happy with product. Hope this helps.