Quick transmission question

[Furious 64]

What's the difference between a 18 spline and a 23 spline 4 speed transmission? I'm restoring a 1964 sport fury with a 440 in it and I was wondering what the differences in performance are, if there is any and what you guys would recommend. Just need some general information about them.
Thanks,
Tyler

 

[Pops1967GTX]

Some nice information
http://www.brewersperformance.com/orderinfo.htm

http://www.hemmings.com/mus/stories/2005/03/01/hmn_feature17.html


http://www.crankshaftcoalition.com/wiki/Transmission_identification