You all have me thinking now. I should probably do the exhaust on my Y88 too. Mine is all original and even has the original cat. Only 45k miles on it so it's in great shape, so I should pull it and save the system for later on. I was planning on the RA manifolds as well, but it get's pricey if you want the splitters. On my last Firebird, a 79 base with a small Chevy, I ran the Pypes from the headers with the street pro mufflers and the straight out the back pipes. Installed myself and it sounded great.
Hope your wait goes fast!