[Brad54]

Mid-to-late '80s Chevy trucks had a 4spd manual OD available. It's a Chrysler/GM hybrid trans. 4th gear is .73:1 (or .72, depending on sources). 1st and 2nd gears are roughly the same as a TH350, 3rd is 1:1, 4th is OD.
Some of them use a standard Chevy bellhousing mount (I have one of those in my '61 Suburban), and some cases had a Mopar mount and require a specific bellhousing.
The maincase and guts of the trans are the same as the Mopar A-833 4spd OD, but the tailshaft is unique for the Chevy units, and uses a TH350 speedo drive gear set and rear seal.
The shifter was Hurst, and there are two versions available, and they are both unique to the Chevy trans only. The Mopar unit will NOT work, because of the dimensions of the GM tailshaft housing.
Input shaft for the GM trans is standard GM length, spline-count and bushing/nose diameter.

The cases are usually aluminum, but I heard that some were also steel, and finally found one that is steel a few months ago. My preference would be for a steel one, as in the Mopar world, the aluminum 4spd OD cases are known to eventually fail behind lots of power. The problem is the second shaft registers directly in the case, without a bushing or bearing. Eventually, the hole in the case starts to wallow out, and the more it wallows out, the more the gears try to separate while in action, which causes the hole to wallow out more, etc.
The fix is to bore the case to have a bushing or bearing.
Originally, big block Mopar trans cases were cast iron, which made them bulletproof. The Direct Connect Super Stock race case was aluminum, and had a big steel insert bushing in the front of it, for the shaft to ride in. (got one of those in the shop here, too)
-Brad