Vapor-lock: Fuel vaporizing in the fuel lines, carburetor and/or fuel pump, causing disruption of fuel flow.
I don't remember ever having a vapor lock With a Chevy, or Ford OHV Six, but have experienced it with both flathead V8/6 cylinder Fords and a VW.
I've found that, with an insulating spacer under the carburetor and aluminum foil wrapped around the fuel lines, (that pass anywhere near the engine) the problem ceased on the Fords.
I'd bet that stainless covered fuel hoses would be neater-looking and even be less prone to heat-soak. Routing fuel lines as far away from the engine as possible would surely help, too.
Restricting the exhaust flow through the VW intake manifold heating pipe and insulating the fuel lines prevented vapor lock in my '67 Beetle.
I suspect the heat-riser being inoperative as one reason for excess heat on inline intake manifolds. If it is stuck in the open position, the exhaust will continue to heat the intake even after warm-up. I've never seen a vapor locked engine with a water-heated intake.
I notice that with Flathead MOPARS, the fuel pump is close to the front headers and exhaust pipe. I would think it'd be prudent to make a shield to go between the fuel pump and headers and design it so air from the fan could draw heat away from the pump. I'd insulate the fuel lines, too.
