I don't know what those letters / numbers mean. I think that's one for BobW to answer! �;)
Here is a pic of the transmission from my 1951 CJ3A. You can clearly see the date cast on the side of it "5-2-51." Maybe you can get a look at the side of your T-90 and see if there is a date embossed there.
I picked up another parts Jeep today and the tranny Date code by the shift tower is K 272 2. Can anyone tell me what tis means. I am positve it is a 3A as the engine mounts are offset and it has the D44 rear. After I get rid of the DJ rust bucket body that the PO put on so plowing would be more comfortable I will know more.