I just did mine a few days ago. the bolts are 11mm.
I have every extension available. the only thing i used was my bare hands and unscrewed the bolts by hand. if you have small hands it will be the easiest way to do this.
If they are on too tight then use a 1/4" drive ratchet with a short 11mm socket and wiggle it around the bellhousing and onto the nuts. break them loose then use your hands to unscrew the bolts.
I have done this twice now, each time took a while since it was pitch black outside and was only using a flashlight. Oh and the last time i did this, the one bolt did fall through the housing, unscrew the two 14mm and two 18mm bolts on the flywheel cover and simply retrieve your bolt/washer.
A suggestion if you have good light and some extra time.(Next time I have to do this i certainly will)
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If you use a dremel and cut the holes on the new cps open making them a half moon shape, you would never have to actually take out the bolts again! just simply slip the CPS out of the housing and slide it back in.