Soak them with penetrating fluid and let soak for a lil while. If you have a dremel and/or an air die grinder, put a small cut off wheel on there and cut a nice slot in the top of them and use a BIG slotted screw driver to turn them out. But give them a couple good hits on top of the screw driver before trying to turn them out to loosen them up.
If that don't work for you, get a pointed punch and hammer and hit the right side of the slot you made on the top of the bolts with the hammer and punch and they WILL break free and start to turn.
And if all that don't work, but it will, get a torch and put some heat into the bolts (not to much to burn your house down though ) and they will come out right away.
Only thing though, you will have to get new bolts if the slots get fuct up or stripped more.. Can get new bolts at the hardware store or even better, get the allen head bolts for the clutch cover for like $5 at RMATV, never strip them again.
Good luck