You know Flibuoy, your right. I looked. The jtr book doesn't really explain this. My apologies.
Here is my experiance. I bought a '91 T5 out of a Firebird. It has the 15* tilt. The place where the tranny mount bolts up is cast at the same 15* angle. So when I bolted the f-body belhousing to it (also at 15*) the tranny mount comes out level. I just bolted it to the jtr mount. no bending, cutting, or folding needed. Now, if you are using a T5 from another car that is mounted straight up, and the f-body bellhousing, or vice versa, then I can see your problem.
Again, sorry if I sounded patronizing, just seemeed too simple to me. Either way, I could have come off better.