Short version - I can't get my truck this weekend but crawled all over it trying to find a stamp or number. Couldn't find anything near the top of the bell housing on either side. The only number I could find was a stamp just above the fill plug inside a circle with a line through the middle, 76 over 15.

Long version - went to go get my truck and the shifter and my spare tranny were locked in the repair shop... Not only that but the tranny shop put a bronze sleeve in to replace the plastic bushing and now my 12mm socket and extension won't work as a shifter, so I just left it. Probably try and get it Tuesday evening.