You do not need to grind a b-h to correct for squareness....

The thru bolts that come from the front do affect the squareness of the trans to b-h surface. Try tightening or loosening them using a torque wrench with an indicator that reads =/- 0.00050 or better yet 0.00010. The amount of torque on these bolts affect squareness, Period.

This is where you would shim if the squareness needs correction. Yes you can shim, but how you shim, with what and where are important.

Using studs instead of bolts is also a very good idea, but as always these good ideas usually end up in the trash along with proper measuring.

Squareness affects shifting and proper clutch operation......