Ben, try PB Blaster on the bolt, if you can get the penetrant down the shank and maybe seep into the threads. Once a day for a week, maybe, then try rapping the bolt head with a hammer, it may break the threads loose. Save the metal you've already cut of the car, you may need it later on to help fill the holes. Also, check the manifold bolts location, you may have to put in an access panel to get to them like I did. Also check location of other attaching hardware, on Willit? in order to get to one manifold bolt, the starter had to come out, so I made provisions for that, too. As long as the engine/tranny is like a yo-yo right now, it's a good time to look for that stuff. It's easier to put in an access panel with the engine out. Same for the stuff up front of the radiator.