I am trying to decode a tranny in a friends 68. It is still in the car and hard to see the numbers. I will post what we can see and hope someone can help decode..
Numbers seen are as follows..
31J8
AF 02
8313 GM
3925658?

Hard to see so some are questionable...

Anyone able to offer any insight?

Thanks in advance for any help!

...not sure about most of those numbers (they seem to be just the PN castings), ...however if the "31J8" is stamped, ...I believe that's the date code... but it doesn't make sense to me.
I thought the saginaw's would be like 'R7J18', ...where the '7' would be the model year, ...J the month and 18 day of month. Are you sure on the numbers you have "31J8"?

It was hard to see the numbers with it still installed, but I believe these were correct.