Hot Rods Decoding stamping on a TH350 transmission

I have a TH350 that is stamped 17Z479208. I believe 1=Chevrolet, 7=1977 and 479208 is the last 6 digits of theVIN but can’t find anywhere what the Z designates. I think it may have come out of a pickup. Any decoding gurus out there that can help me? I’m guessing the 1 & 7 probably tell me everything I really need to know but I’m curious.

 

Z would be the vehicle assembly plant

Z was Fremont CA back in 1977. I think they made trucks and full size cars there.

 

Super. Thanks