It is the angle in-line from engine front, downwards towards to the IRS diff (6.0 or 5.3 V12).
I am making a new bespoke gearbox cross bracket and forgot to record the angle before I sold the old 6.0 standard trans mount.
It looks and feels right at about 3 degrees down and the IRS is 1 degree up (not rebuilt yet, so still on old suspension.)
Thanks