Change from 23 to 18 spline clutch disk

Never mind, misread your post

I don't know if anyone currently makes a 10.5 18 spline BUT I'D BET THEY DO

The 11pp/ 10.5 disk is incorrect. Some of the 440's (My 70 six bbl example) used a pp with a 10.5 BOLT PATTERN and then the outer edges of the pp mounting tabs were "scalloped" to allow room for a LARGER than 10.5 disk

These disks have been called various things through the years, including 11", 10 7/8, 10.XX and so on. THEY SUCK. I had a lot of trouble with mine not wanting to release clean

Sounds like what you want is a HP aftermarket 10.5 setup in 18 spline

Here's an old thread. You have to click on the photos to display them

I'm a little confused about this clutch.