I've rerouted the coolant flow in a miata based on a project on the net. Some things i picked up from the mod:
1)Copper tubing conducts heat better than stainless and is easier to weld.
2) you'll have to put a "ring" on the copper tube as a stopper for the clamp and to prevent the rubber hose from sliding off.
3) look for a brass fitting to house the thermo switch rather than a simple nut.