Tim,
I don't know if this helps:
The
1961 Chevrolet Truck resto pack from GM Heritage Center.
Shows on pdf page 10, Engine ID, JB and JH
JB, was stamped on engines in C 10-20 series trucks with RPO 311
JH, was stamped on engines in P 10 series trucks with RPO 311
Now go to pdf page 30, "Regular Production Options" page
It shows 311 Powerglide transmission, C 10-20, P 10
I think the Powerglide RPO number for the passenger car
were different than the Powerglide RPO number for the truck.
313 car
311 truck
I have even seen a 317 Powerglide RPO for early 50's passenger cars.
So it seems the Powerglide RPO number changed periodically depending on what the application was, truck, car, year.
I'm not sure, but I think this is what you were looking for.
