When I was trying to determine my transmission etc. I asked in this post.
http://forums.performanceyears.com/g...152#9126066152
Your may want to try that but you mentioned yours is from another vechicle. Do you know if it's a TH350 or TH400?
Here's is a copy and paste from the above link.
Goathead68, good info, but one error. The partial VIN used on the engine and transmission starts with "2", which means "Pontiac". What they actually used was the VIN minus the four-digit model and body style numbers.
242379B100001 would be a 69 GTO coupe.
2 = Pontiac
42 = GTO (model)
37 = coupe (style)
9 = 1969 model year
B = assembly plant
1 = V8 engine
00001 = build sequence number
So what you're looking for is the VIN minus the "4237", and it would look like this:
29B100001
** I found my tranny vin right by shifter linkage boot. As per pic below
->KB<-