like the choice of housing for a race car; I see so many cars with housings that are more for an unlimited class offroad truck, so keeping that unsprung weight down is a smart idea. Did you have any camber welded into it? Circle track guys get around -0.5 deg neg in the rear without too much funkiness with the axles. I have heard of around -2 deg but that takes some special parts so the axles don't bind. Not sure if you have messed with any of that.
Have you put any thought to moving the exhaust tips into the rockers (french them in to be even on the bottom with the rest of the rocker)? It would look pretty cool IMO and more like it is part of the car.
There was a 69 Camaro in Popular Hot Rodding June 04 from the NorCal area now that I think about it. I have a fistful of magazines I have kept as inspiration whenever I think about a project and that is one of them so I just pulled it out of the drawer. Big flares, Nascar setup, but had a big wing on the rear I wasn't a big fan of visually. Your rendering reminded me of it and I prefer the look of the spoiler.
found a pic on the Hot Rod site, PHR blocked theirs.
http://www.hotrod.com/featuredvehicl.../photo_01.html