On my daily 235, I got an aluminum 2x1 intake with exhaust heat from fentons via the tubes.
I don't use carb spacers and never had any fuel delivery issues. Even going down the freeway for hours in August desert temperatures.
I believe only cast iron intakes require the spacers to prevent boiling of the fuel, especially when parking after a hot run.
On my current 261 project I will use the fentons that attach directly to the manifold.
Most of the heat comes from the direct connection, like with the original single intake/exhaust.
There is no heat riser baffle on these fentons, but the 2x1 aluminum intake only has a small heat chamber under the two carb's section of the log.
I think it's best to give these dual intake manifolds for street use, as much heat as possible.
What early fuel savings device patents have in common is to preheat the fuel before the carbs to improve atomization and give more efficient combustion.
High performance engines with triple or more carbs don't use additional manifold at all.
