Thoughts on completely blocking off the heat crossover; If you drive in northern latitudes other than right in summer, carburetor icing could be a problem.
It doesn't have to be freezing out to have carb icing, due to venturie air velocity. And if the exhaust manifold divertor is disabled  & the crossover completely blocked, isn't it going to at least partly disable your chokes operation? (assuming the choke isn't electric)  Unless it's a race engine, the truck semi closed gaskets might be a better idea ?  


Paul

truck int gaskets ar restricted by 50% and are usually in oh kits