18 VS 23 spline

The 8-3/4/DANA debate resides else where here. The bottom line is the 8-3/4 is fine for the street or light to medium racing. Nothing heavy duty. That's what a DANA is for.

But since the thread is actually about the 4 sod trans spline count and its worthiness or not....
I have had my E-body Cuda with a standard stroke 360 up and well over the 440HP mark and it is fine in the street with very little track use. Street tires and S/S springs, Centerforce Dual Friction clutch.

I don't know where the "Give up point" is on these transmissions, but if it is going to be "Raced", a Jerico is a good idea. (Along with a DANA.)