As for the exhaust, i had the same exact problem a few months ago, if your talking about the two studs that are in a flange on the manifold that hold the front exhaust pipe. I ended up trying to get it off and the stud snapped so i had to take off my exhaust and intake manifold to put it on the drill press to remove what was left of the stud and place a helicoil in its place (its held up really good so far), with new stainless steel hardware from a local hardware store. The first thing i suggest is to get PB blaster and spray everywhere around the threading where the stud is and let it sit for a little while. then spray it a couple more times letting it sit and soak into the threads. I used a Stud/bolt Remover kit that i had in my toolbox to remove the other stud after it was soaked in PB blaster. It might also help to use a breaker bar on your ratchet to get more torque out of the ratchet.your going to want to replace your studs with stainless steel because you to wanna avoid all rust if you have to do work again in the future. to replace my exhaust, i picked up a walker front pipe, Dynomax Cat, Stock muffler, walker tail pipe from my local parts store. If you have to remove the manifold replace the gasket if you haven't already and also coat the threads with Anti-Seize compound to prevent stuck bolts.
1987 YJ, 4.2L I6, Weber carb, 4in. RC lift, 33x12.5x15 BFG KM2's, 15x8 Cragar soft 8's, custom steering box skid, and more