Transmission on my 1980

[d_hache]

Hey guys, i know someone here will have the answer.
I pull out the tranny from my 1980 Trans Am.  (The car is being restored)
I know the tranny is not original to the car but i am trying to find out what it is and where it came from.
Previous owner told me it came from a 1981 Pace Car. 
I see 2 codes on it that are visible, there is a smaller one that i cannot read that look like 4 digits.
Thank you much.

(Codes M38 and D6)

[Wallington]

It's a BOP Th-350 auto, so suits a Pontiac and not a Chev. Couldn't tell you if original to what or if was a Turbo. Some had engine number stamping vertically on the tail extension and date code/factory on pan side, but not always. There should also be a year casting number with circle around in on the bellhousing side fwd of the gear selector lever.

[d_hache]

Great thanks allot for the info