3 speed tranny need help deciphering codes/stampings

[Hennyhog]

Hello All,
I've been on the web a good portion of the morning on various websites trying to decipher what I have in my 71' C-10. All I know is it's a three speed with a Hurst shifter.

Pretty sure the picture with the GM 1 stamp the numbers above it are 3811942 or 8811942 with E 29 under the GM 1. The other GM 1 has 9952882 under it.

Any help you have would be a big help!

Thanks,
Henny