8617230 is the cast number for a Hydramatic Transmission case.
In the Chevrolet Master Parts List it says:
58-62 All with H.T. (2nd. design) (exc. 1/2 ton) part number 8617232
I have no GMC parts list but this transmission case was probably used on a GMC as well.

Look at the other side. There should be an oval tag with serial numbers.
On the torus cover there should be a rectangular tag with the engine serial number (engine and transmission are matched).

Last edited by buoymaker; 04/23/2022 7:22 PM.
"Adding CFM to a truck will only help at engine speeds you don't want to use."
"I found there was nothing to gain beyond 400 CFM."