If that has the large shaft a-body mainshaft and extension housing, that's a good find all by itself being aluminum, unless it is an overdrive. Please explain further kind sir? Do you mean input mainshaft?
Don't know what 'input mainshaft' means. I was talking about the output shaft (mainshaft). The input shaft is a seperate piece, known as a main drive gear.
Most of the overdrive a-body OD units I come across has the small spline output/small X-housing. Also, the four speed mainshaft is different than a OD mainshaft. I've got several small spline, a-body 4 speed output shafts here , the 30 spline 4 speed output a-body shafts are harder to find.
The A-833 OD units found in GM vehicles have a different input shaft for the GM, and the case bolt patern for the bell housing is different. All of the GM overdrive units I've seen have a cast iron case, but I'm not saying they didn't make them, I've just never seen one.
Russ.
Edit: What i was refering to in my last sentence was aluminum cases for the GM OD transmission. Sorry 'bout that!