I spent about a grand on it, could save money if you can find a surplus valve.
I posted pictures on the Ford forum about a year ago.
Get a 20 GPM closed center load sensing (CCLS) control valve, I got a prince with a joystick kit.
Get a shuttle valve for the sense line.
Tee into the line on top of the transmission for the supply.
Tee into the small sense line on top of the transmission with a shuttle T.
Others know about doing this too.