Rounded bolt head on dbl. cardan joint - help

I started in on removing the tranny & xfer case today, in preparation for R&R of the slave cylinder on my '92 XJ, and I've run into a problem. In removing the front driveshaft from the double cardan joint, I rounded the head on one of the 5/16 bolts securing the shaft to the DC joint. (Should've started with the 6-point mini-socket instead of the 12-point flat box end wrench!) I've got the other 3 bolts loose, but am stumped as to how to proceed. I can't drill it out, as the collar of the DC joint prevents me from getting anything near a straight shot at it. At this point I figure my best bet is to just drop the drivetrain with the front driveshart still attached, but I'm hoping someone here has a Geewhiz idea to get purchase on the bolt. Would it work to press the U-joints out while it's on the vehicle? The bolt head is also size 5/16, so there's not much material to apply any amount of torque to, were I to cut a slot in it for a screwdriver. Yeah, I should've hit them with penetrating oil yesterday, or a torch today, but it's too late for that now (although I did both before trying - unsucessfully - one last time). I'd be grateful for any ideas. FWIW, I did a search and the one result didn't address the remove-the-u-joint option. Thx,
- Joe

Small grinder...take off the head of the bolt and it should pull through. Once it is out of the vehicle, you should be able to get a good bite on the piece haning out with some vice grips or worst case, then you could drill it.

Just be careful with the grinder not to damage the joint to much...mostly worry about the bolt surface...don't want to chew up the surface so that the bolt head won't sit flat.

Good Luck.

I use a tire iron through the U joint to pry it just slightly (enough to stretch the bolt, but not to break it) then put 2 of the other bolts back in tight. It tends to come out pretty easy after that!

tool manufacturers make these nice things called "vice-grip plyers"

yes i know it must sound weird but they are used exactly for this application. get some. and yes they make small ones that will fit.

Thanks guys! I'll try stretching the bolt first. At that point, it might be loose enough that I could get it loose with vise grips. And if that fails, I'll use the dremel to grind off the head. Much better plan than what I was contemplating! I appreciate the ideas.
- Joe

FWIW, when you get to the rest of them, I had a lot better luck with 8mm than 5/16.