Had this happen twice and did two things:
First time used a torch to heat the studs, then vice grips to slowly work them out. Took a while, but tapped and used new studs/bolts.
Second time was on a 93 that was rusted TO HELL! No way I was working out those bolts. Used a torch and plasma to cut new holes and used new bolts and nuts.
There is no way I could drill out the old bolts, not enough room and too hard of steel. I was using Cobalt bits, got nowhere fast.
Best choice for the two was the torch method, jsut had no choice with the 93.
2001 Ranger with some stuff (RIP, some pieces still floating around)
2004 Level II and an 05 Rubicon with some stuff.