Upper hose is collapsing!

Took another look at your photos for clues. Before you try my metal tube idea, try re-routing your coolant recovery hose behind the radiator. I'm thinking it may be getting smashed flat on the radiator support when the hood is closed.

Vapor lock is usually caused by fuel percolation. I see your metal fuel filter laying next to the passage that carries water into the engine. Try to insulate the fuel filter with a couple of pieces of old radiator hose. There's not much room, but if you can bend the metal fuel line away from the water pump and cylinder head, it will help.

Also check when vapor lock has occurred that there is no restriction in the fuel line. I had too much flexible hose between the rear fuel line and the fuel pump on the /6 in my 73. When it got hot it collapsed. The problem was cured when I shortened the hose to account only for a minimal ammount of engine rocking.

Hope this helps.