I have fitted a water by pass system to the Ford 250 and it is now ready for a run but I still have to fit the electric pump to get the volume of water through the head so that the temperature variation through the head and block is reduced to under 10 deg C. In the normal mode the temperature can be around 40 deg C variation and this causes many problems.
Darryl was involved in the research with this system some years ago and claims a possible increase of up to 30 % in power and efficiency.
It would be a good idea to check your engines to see if they have in fact built in a by pass system and check to see if the water flow is a minimum of 10 litres per minute at idle. As the revs increase the flow should also increase. The great advantage with having the thermostat in the lower hose is that the water flow is not inhibited and can flow freely around the head at all times eliminating hot spots and steam around valve seats and off course all the associated wear.
Please see the video clip below.