For me the exhaust minifold bolts have always been a major pain. Poolguy is right on the money. get yourself a drift/punch or even another bolt; probably 5/16" x 3- 3 1/2". There isn't much room to swing, but put the punch etc against the bolt head and then hit it several dozen times as had as you can. A lot of times this will allow you to get the bolt out. Otherwise go buy a MAPP gas torch at Walmart, Home Depot. get the Mapp gas not the propane. The MAPP gas is a lot hotter. Be careful with it and have an extinguisher ready!! Oil that has leaked, rubber or cork gaskets etc tend to go up fast. Another thing I have found is heat the bolt cherry red, let it cool and then heat it again, cool it and then heat a third time. Immediately after the third heating try your long breaker bar. Good Luck
Swamp