If you're doing anything other than removing the transmission, you'll need to pull the dust cover, so whether or not the holes are threaded is a moot point. You could epoxy some nuts to the inside of the bellhousing, I suppose, if you want all the bolts to go in from the rear. Be sure there's no interference between the nuts and bolts and the flywheel/clutch assembly. The thread size is 1/2" X 13, standard-thread 1/2" bolts. I don't think there's enough metal in the T-5 case to cut 1/2" threads unless you install Heli-Coils in the case. If you want threads in the bellhousing, just use 1/2"X13 HeliCoils in the bellhousing. The thread inserts will hold better in the cast iron bellhousing holes than they will in the aluminum T-5 case.
Yes, it's necessary to pull the pressure plate, clutch, and flywheel, in that order to get to the bolts that hold the bellhousing on.
Jerry
