Don't heat the bolts that causes them to expand. You need to heat the metal around them.

Curtis

you need to drill them out. Center punch the bolts and drill a 3/8" hole thru the bolts and then use a 3/8" bit to drill just till the heads are drilled through and chizer the heads off. Cover the gears so no chips get in and use a 1/4" drill do drill through the remaining bolt shanks and use an easy out to remove them. If they still will not come out try opening the hole up a little more and retap the holes.

After getting it hot hit the bolt with a hammer to try to free it up a little before trying to unloosen it. If none of this works I guess like others have said drill it out or use an EZ out. I always use an impact on my rearend never any issue's but I have had it apart many times.