The beauty of the B/RB wedge for jet boat is you can use the front cooling ports for inlet/outlet or the lower block drain plugs as an outlet. Outfitting a T-stat is a bigger problem. There's ways to fab up a housing using a Brand-C marine T-stat housing.

If you really want to run an "enclosed system", simply learn how to use a TIG welder and make your own aluminum radiators then mount them into the side gunnels, w/remote elec. fans, or one big rad. mounted in back. Either way it's a fab all deal.

My 18' jet runs the coolant in through the front lower cooling passages and out the uppers. It has an old Edelbrock marine set-up. The key ingredient is to monitor your system pressure. With a closed system, an aftermarket electric pump (Mezuirre sp?) like the drag racers use might be the way to go. Jetters typically use a pressure by-pass regulator since pump pressure can get as high as 200-300 psi.

V-drives rule but jets are far more cost effective and easier to maintain.