Inpu needed - Strange Muncie stamps

[L16pilot]

A friend of mine sent me the below photos of a Muncie...and there's a couple of weird things going on here and would appreciate anyone who may be able to shed some light....so here goes:

1. The main case is a 660 and carries an April 9th, 1969 assembly stamp....so far, so good, but the assembly stamp carries a suffix "BD" First assumption is it is an M21 based on the "B" designator, but has anyone seen the extra "D" character before? Any clue as to its' meaning?

2. The VIN and all other characteristics indicate 1970 Pontiac Firebird built in Norwood. There are no other detectable VIN stamps on the case and the surfaces appear virgin.

3. This trans carries the correct 1970 3988011 WL tag on the side cover, but there is also a little metal bracket under the side cover bolt next to the TCS switch I am not familiar with...anyone recognize this?

April 69 is in my mind, way to early for a carry over trans case, so I am thinking maybe someone had a 1970 Firebird/TA, broke the main case, so found a replacement used case and used everything else to make up a new trans, but wanted to see if anyone has any other theories as to how this came to be....

Thanks in advance for everyone's input and help.