well removal was going great until i got to unscrewing the nuts at the heads. 3 of them came off ok, but when i went to do the fourth one (which also happened to be the rearmost one) before i even put the wrench on it i knew something was wrong. so i touched the nut and found out the it was rusted away from the threads.
so now, the threads are still in the hole without the nut, and i wont be able to put a plug in there.
any suggestions, and how big of a problem is this?
Have you ever used an Easy-Out? It's a type of left-handed drill bit that grips as it turns counter-clockwise. The only problem I can see is having anywhere near enough room to get in there first with a drill, but you could just stick the Easy-Out in the hole and turn it with a wrench! Try putting some heat from a propane or Mapp cylinder on it and some liquid wrench. Good luck!
I suppose if you're having too much difficulty you could remove the exhaust manifold completely to get at it, but then you run the risk of breaking off a manifold bolt, which would be far worse than the situation you're in now. Good luck!