The only aluminum exhaust manifolds that I ever saw for a W was from the aftermarket.I think Bob Walla had some at one time but I don't know if he had them made.
I don't know about Jet Hot but I bet one of those thermal barrier coatings they use on piston tops would if they can figure out how to get it inside there.I don't know if I would coat the outside it might interfere with rejecting heat to ambient.I wonder if jethot coating inside and out would help the aluminum manifolds.