I am pretty sure you can keep any cat back exhaust system on the car with long tube headers, I am told there are a few y-pipes out there offered for the long tubes that bring the headers back to a single 3 inch outlet so cat back systems can be used. I believe ORY is one manufacture of these y-pipes.
As far as headers go I have been contemplating the same thing, and after being here a while and asking similar questions, more often than not the same name keeps popping up,,,,,Pacesetter long tubes,,,,they seem to be the favorite for most people here. Whether it's because the price is cheap compared to others or the fit it good I cannot say, I will leave that to others on here that actually use them, but if there is a better fitting header out there it would make sense to me to spend the extra money for it. I think the biggest issue for me is,,,,are the plugs any easier to get to?
Do a search on Pacesetters and ORY y-pipes, although I suck at the search thingy,,,it may bring back some answers for you that your looking for. Larry.
70 ram air Formula
72 SS 454 Chevelle
71 454 Corvette
97 Z-28 6-speed Convertable
88 Iroc 350 TPI
79 Chevrolet 1 ton 454
79 Monza 406 sb
82 Jeep Scrambler (96 LT1, 4L60E)