The mid drive axle difference might have less to do with the material and more the vintage.. Mark had an older 35 speed Pursuit and the later ones I believe had 49 speeds.

Perhaps but it was clear that the Ti machine has a round tube with the axle having a through threading out the opposite
side from the mid drive cassette, where the steel machine had a square tube and according to mmatarella the axle threading
was not all the way through the square tube. So not only is the length of the axle different the Ti mount allows lock nuts on
the opposite side from the mid drive cassette where the steel tube axle bottoms out on the inside of the mount tube if I
understood mmatarella correctly.

I only ever saw one Rotator, but I don't remember it being square tubing. In fact, I even found the pic.

https://cimg0.ibsrv.net/gimg/bikefor...3b41e6e024.jpg