A833 4-Speed on a 4-500hp 440: 18 or 23 Spline Necessary?

I'm putting a 23 spline iron case behind my 383, maybe 450 hp, my buddy had one in a 4100lb c body with a 440, ran 13.0 with 3.73 gears...he beat the crap out of that thing and the trans never let go.

but if you have 18 spline trans money it certainly wouldn't hurt to have it