If you plan on removing the bent stud, I recommend that you heat stud with a Mapp gas torch until it turns red where the bend is and straighten it with a piece of iron pipe which just fits on the stud.
At this point, I would look it over good to determine if the threads where the nut will ride is still sound.
If you determine that the threads are too far gone, at least now you have a straight stud to work with to put the proper force on it to remove it.
I'd double nut the very end of the stud, heat the manifold and the bolt, then strike the end of the nut with a hammer.
I'd then very carefully try to turn the stud clockwise until you feel the slightest of movement, then carefully turn it counter clockwise until it moves slightly.
Now you cam turn it back and forth as though you were using a tap to tap threads. Once you get some movement in both directions, penetrating oil will be able get in there and do its job.
Do all of this like you have all the time in the world.
