Drill the CV joint and tin boot retainer for the other two bolts.
This is easy, ends up the same as the ‘928’ CV joint and doesn’t cost anything.
Having six M10 bolts is very desirable.
If someone has the answer to the spline size inside the early 108 mm CV joint and the ‘late’ (928) 108 mm CV joint, please post the details.
This is a very worthwhile thread:
http://forums.pelicanparts.com/porsche-911-technical-forum/222537-reconstructing-constant-velocity-cv-joints.html
Long but worth studying.
Rember to use new Schnorr washers, torque to 63 ft-lb and again after about 100 miles.
Best,
Grady