71 up 2.47 to1 and 2.66 to 1

That would be the spline-count on the output end of the Mainshaft.

A-body
A833 overdrive boxes can be found at Swap meets in either flavor.
the slanty-boxes have the 904-sized shaft.
the 318 boxes can be found in either 904 or 727 sized shafts
As to Non-od boxes, IDK but;
All performance V8 boxes have the 727 sized shaft.
As to non A-bodies, I think they were all 727-sized.