Victor,
If you look at the AIM 6 B9 revision record you will see a mount revision, just wanted to make sure no one mistook that revision for the BB change.
I believe the first SB with a T400 was the big pass. with a 327 275 HP around Jan, 67.
3872247 was the first mount introduced on the auto. 325HP 396 but sometime before the end of 67 production it was changed. Why and when I am trying to find out.
You are correct about the BB support assy. 3912573 and CRG has a good report that addresses that issue.
Bob