I tried this back in 2010 when I had the TKO600 and McLeod twin disc in the car because of breaking parts and having a hard time making radials hooks. It has some merit and sorta worked but I finally gave in and went to a 4R70.
The only things I did different was I put a pressure switch in the system and a micro switch for 1st gear to keep the 2 step active till the pressure bled off a little in 1st gear. After 1st gear the system was bypassed via the solenoid valve.
This is the write up I did on another forum. I deleted the pictures from my photo bucket account but may still have them on another laptop if you are interested.
Hydraulic system.
1) Line lock solenoid to force fluid through the flow control side of the system.
2) Directional flow control. Allows full flow to the clutch T/O cylinder but meters the flow of the fluid back.
3) Adjustable pressure switch that stays closed while the pressure is bleeding off and is connected directly with the 2 step so that the engine RPMs are controlled while the clutch is slipping.
Electrical system.
1) Spliced into auto transmission plug in the console to get a keyed 12V supply for the relay and switches.
2) Installed a toggle switch on the side of the console that allows the system to be turned off for street driving.
3) Mounted a micro switch on the transmission that is closed only when the shifter is in first gear.
4) Mounted a NO (normally open) pressure switch in the system that activates (closes) when the hydraulic pressure in the system is greater than 200 PSI.
5) Connected the NO side of the pressure switch to the coil side of a 30A automotive relay that will power the line lock solenoid.
6) Connected the 2 step rev control into the pressure switch so that the 2 step is active while the pressure switch is closed.
So here is what happens.
When the car is brought into stage I can activate the system by turning on the toggle switch. With the clutch pedal depressed and the shifter in 1st gear the 2 step becomes active and will hold the engine RPM's at the set launch RPM. I can dump the clutch and the flow control meters the flow of the fluid returning from the clutch cylinder. This allows the clutch to slip for a few tenths of a second and lets the car get rolling with out that violent shock. The pressure switch in the system stays closed until the system pressure drops down to about 200 psi. (When the clutch is pushed in the system pressure is 960 psi with my clutch) Below 200 psi the switch opens and the 2 step drops out. Shifting, clutch application and rev limiting after 1st gear is normal because the system drops out as soon as the shifter is pulled from 1st gear.
The flow control is going to take some time to get properly dialed in. First indication after a few launches at the track Sunday is that there is some potential for the system to help but it is going to be very track (traction) sensitive.