I don't think you can get vapor lock on the discharge side on this car. The carb is probably a Carter (or Holley if it's been replaced) and are just vented.

The metal fuel line on my '66 Chevy is anchored to one of the exhaust manifold bolts, and it has no fuel problems. The alternator is bolted to the other exhaust manifold. GM is such a wonderful company...

I'm sure it's your filters. They all use the same filter medium, so the smaller the filter, the higher the pressure drop. Gasoline also changes it's vapor pressure by a couple of psi from cold to hot, so it's reasonable that, if it's marginal on cold days, it'll lock on hot ones.

I'll have to ponder why the lock persists for so long. I have a '92 Volvo that vapor locked on me recently. It has a totally unnecessary in-tank pump and a much larger pump near the tank under the car. The in-tank pump died and became a massive pressure drop in the line. The main pump vapor locked (it's lower than the tank) and it did take about five minutes to clear.