Here's a good article on proportioning valves: Samurai 4-wheel disc although reading around seems most people opt for the 50/50 split, which means just bypass the existing valve. For safety reasons, I'd do some experiments with and without the factory valve connected.

-Todd
1987 Montero 2.6l 5-speed (Sold...but I still miss her)
2008 Jeep Patriot Sport 4x4