18 or 23 spline with 440?

Hey, i'm converting a 74 swinger /6 904 into a .60 over 440. Even though the 18 spline A833 is called the hemi Tran, I've heard that anything over 383...especially 426 and up should use the 18 spline. Its this completely true? This car is going to be a showroom car with the ability to kill it at the strip as well. Thank you for any insight to this.