Safety wire

If you can drill bolts properly, fine. I suggest you purchase US-made bolts in Grade 5 rather than trying to re-use the stock bolts. Reason is, the stockers are hardened all the way thru, making them rather brittle for this application with its heavy shock-loads. In addition, the stock bolts have Euro-type serrations under the heads, which tend to 'cam' over tiny obstructions on the fairly hard ring gear face it tightens against, allowing some bolts to make the preferred torque but still be loose. I also suggest you use 0.032" dia stainless steel safety wire, so the required hole will be big enough to easily clear that diameter. Note that all this stuff is in the vendor kits....

As to your last question, the bolts are 10mm x 1.0, 7/8" long; ten are needed. Torque to 70 ft-lbs in a cross-pattern in the usual manner. The ZF overhaul manual also recommends using Lock-tite (type unspecified, but I like the red). Very high torque passing through, long times between services and being submerged in hot gear-lube all add up a truely severe operating environment for these bolts. IMHO, a crow-foot socket is the only way to torque these bolts, and a SAE crow-foot (I forget the size) will fit closely enough to reach torque without damaging the metric bolt heads. Good luck.