Exhaust bolts

Hello. I am sorry that this isn't about a Blazer. They don't have a spot for my car and everyone here has helped me before with my Blazer. My muffler broke off of my Geo Prizm today. I got the new one and tried to get the junk piece off. I had to take the rear tire off to get at it. I got the bolts to turn after using PB Blast and a pipe on the ratchet. So the bolts turn but the nuts are not budging. The heads started to strip. Vise grips do no good. I have the independant rear suspension, trunk, and gas tank right there so there is little room. The bolts go through the flanges because the muffler, tail pipe, and the pipe with the flange are a welded assembly. If you have any advice, I greatly apperciate it! Thank you!!