Regarding wolffcub's helpful observation regarding "circulation" in the intake manifold:
True circulation can take place in an Offenhauser or Clifford intake manifold.
True circulation does not take place in the Fenton manifold.
The Offy & Clifford intakes allow coolant circulation in one side and out the other side of the intake. "in one side and out the other side"
The other design of intake (such as the Fenton) does not allow side-side (in-and-out) circulation of coolant-fluid. It allows "contact" heat transfer. Using a two-tube heat plate and a tube from each exhaust manifold, should allow adequate heat for the carbs with this design intake manifold (it has worked for me with at least three dual-carb combinations).
By the way, maybe someone who knows about older "hop-up" equipment for dual Fenton exhaust manifolds knows something about the Fenton heating component kit that supposedly used some sort of valve system to allow exhaust gases to move up to the intake manifold, and then somehow allows gases to move down (away) from the intake manifold.
It is too bad that there are no repo Fenton dual exhaust manifolds that bolt up to the heat-plate opening in the intake manifold (as some earlier Fenton dual exhaust manifolds were designed to to).
