My uneducated understanding about needing a heated intake-manifold is that heat is needed at all times; and, the heat transfer through the head to the manifold (when the engine is warmed up) is not sufficient to keep gaseous fuel from condensing in the intake manifold right below the carburetor(s) (caused by latent heat of evaporation).
Many people who have used unheated intake-manifolds (including myself) have experienced acceleration hesitation, even after the engine has reached operating temperature. This hesitation has disappeared after water-heating or exhaust-gas-heating the bottom of the intake manifold.
I have used a water-heat plate with excellent results (Offenhauser dual-carb intake). I have recently installed an exhaust-heat plate that seems to work fine but I have only used it for one short trip (Fenton header to Fenton dual-carb manifold).
If I were working with a tube header, I think I would try Stuarts adapter but simple clamp the adapters to headers, and then run tubes (with threaded adapters on the intake side) to a plate on the intake manifold. If the heat transfer is sufficient to prevent acceleration hesitation, I'd then either weld the the adapter to the headers or clamp them with stainless steel clamps.
