which 833 for a body ?

Just go with a 23 spline a-body transmission.
Don't use the aluminum 4 speed o/d one if you are going to drive the car very hard.
The 18 spline trannys are stronger, but unless you are putting slicks on the car, have 600 h.p., and sidestepping the clutch at 5,000 r.p.m., the 23 spline tranny will be fine.
Maybe phone Passon or Brewer's and see what they think.