23 or 18 spline?
I would do an 18 spline unit for several reasons. The gears are of a coarser pitch and 2-3-4 speed gears are bushed. The input shaft diameter is larger by 3/16 also. I have better luck overbuilding things that get abused. It appears that you have sufficient tire plant to warrant the 18 spline box.
If you are going to regularly powershift it I would look into a face plate 9310 gear set from Libertys Gears.
My all aluminum face plated a833 takes a beating. Email RAM and inquire about a clutch.