Newbie needs transmission ID help

[CousinTone]

Hi all, I'm pretty new here. I've got a 68 & 72 GMC 6cyl & big block respectively and a 64 stepper 6 cyl/3speed manual. I got them as a lot and I have picked the 68 which needs tranny and metal work as the first project. I got it to run pretty good but the tranny sounded like a cement mixer in neutral and the inside was blown up. I got a Saginaw tranny from a great guy on CL but don't know which one it is. The casting numbers on the case are 3987948, tailshaft has various numbers, 3237, 3911 948 GM8 and the tag bolted on the cover is 3968081(either O or Q) Y and the date stamp on the machined section under cover is M2P17A. Can any one help? I have gone batty trying to find the info and I would sincerely appreciate your expert advice. I know the shifters are different than ny column shift, it is a floor shift look. The guy got it for a tool trade and doesn't know other than it ran fine in his 68 panel when he had it in there. Thanks in advance for your help and reading my long, Italian style post.....since I can't wave my hands & arms I write more. Thank you CousinTone.