What does the input shaft look like? They also used the aluminum 4 speed overdrive in gm trucks but it had a different input and I believe output spline.
I am fairly certain that 833 OD boxes, as installed by gm in trucks, were not 23 spline. I believe the input shaft was completely diffefent and coarser.
I think you are correct in that the ones used in the gm stuff was a gm input. The chrysler stuff was chrysler input. I think anyway, I could be mistaken.
I'm going to suggest an OD unit from a "miser truck", being that it has the long tail shaft with the "B" and "E" shifter pad location and an aluminum case. somewhat like this.
It's an A833 OD out of a 1/2 ton or D50 truck, '75-'87. Tailshaft with the B/E shifter locations and the rear location not drilled and tapped is the giveaway.