kind of a side point but there is inlet manifolds that have coolant ports around the bottom of the runners

i dont think you should be needing to heat the inlet though, thats not normally necessary (hence wondering if you lived in cold climate)

with that much work done to the carby, and you sound like you know what your talking about, is it possible the problem is elsewhere? maybe as simple as an air leak in the manifold gasket or carby adaptor

did you remove the bridge on the inlet manifold where the carby bolts down?