I have just been looking at the '54 Corvette intake manifold, thinking about using one.
The car didn't have a heat riser but the intake manifold had the same square heat sink on the bottom and it bolted to the matching cast dual exhaust manifold. There was direct heat transfer between the 2 manifolds. The 3 side draft carbs had a shorter and straighter mixture flow path and wouldn't have required as much heat.