The original FIA used a simple restrictor (with the manifold pictured above) - no thermostat at all - but I don't recommend that for street use. I've fabricated an in-line thermostat that mounts in between the water manifold and the radiator. The manifold with the thermostat housing built-in is a little cleaner installation, and, since the thermostat is right at the engine, probably holds temperature closer to ideal. It's hard to beat the look of the external manifold, though.
