I don't see that working with the larger (18 Gal) tanks because of the hump on the drivers side, 76 & some 77's had that style of tank. The one you might be able to pull that off with is the smaller (15 Gal) tanks because they don't have that hump and are symmetrical (for the most part) top and bottom. My 76 Volare had stock dual exhaust but they both exited on the passenger side because of the tank. I took that off and had a shop tuck it behind the rear tires. Fits but just barely, and my 77 Aspen R/T is set up the same way but it has the smaller tank. So it might be possible to slide the tank over just a little and sneak the exhaust past and out under the rear bumper.
oh yeah, by the way I'm new to the site but not to F-bodys. I've had my 76 Volare for 19 years (My first car!) I also have a 77 Aspen R/T that I picked up about 3 years ago. I've had many others but all were only parts cars (76 Aspen SE, 76 Aspen SE sedan, 77 Volare wagon, 79 Volare Duster, & 77 Volare T-Top)