I would suggest something called "Crow's Feet" which are basically flare wrench ends that you can put on a ratchet extension. To use one, you basically put it on the end of one or two extensions, and ratchet it with your favorite ratchet. Slow going, but really the only way (besides using a flare wrench) to get to some of those lines. Knowing what you are dealing with, I think we are far beyond that (gnarled up bolt you speak of). Depending on the damage, you might be able to get that rascal loose with a lucky fit of a wrench (regular or flare), or you may have to go the vise grip route. Doing the latter probably means you have to take the headers off (again). I hope I am wrong in all this, but guess how I know? Yep.
FYI, there is a certain "touch" when one instals those metal lines. Be it the tranny cooler lines, or fuel fittings. Best bet is to seat the flare end of the line in, then start to tighten with your fingers. If it spins and spins, the line is not straight and the nut cannot start to thread. Re adjust angle of hold and try again. Always get those started by finger, as that is alot more "trouble" accurate vs just wrenching it down. Other times, due to space considerations, you must hold the line back up against the nut, and start the nut, keeping pressure on the line so it is against the nut as you thread the whole thing in.
Sorry for the whole discourse, but its what knowledge I have gained with your problem. Remember, this is "Fun" and not work!
