I'm running a CRT 55X1&2CN. Its a reverse manual with a brake and clean neutral. I really like it. It does feel a little weird pulling it past 3rd but nothing when you get used to it. It is a bit of an investment. I had to buy a PPP shifter for it to work. There may be others that work with it but I'm not sure. My understanding is it's easier on the rotating assembly.
Clean neutral valve bodies are for folks who have aluminum rods as to not decelerate down on the rod.
There are several things that should be done with the transmission when going this route. If you have OEM powder forged drums, you definitely do not want to neutralize your transmission at speed.
Certain 3rd gear piston return springs can also collapse and break apart. We offer chrome return springs for clean neutral applications.
It’s also to help some that “may” have oil scavenging issues on sudden decel/hard braking.
We have a ProTrans brake in our spare 904, and currently running an A&A in the car.