If your line vapor lock is happening after a WOT, its getting heat soak from a header/exhaust pipe. Shield or wrap the fuel line prior to the pump. If you use the corvette vented fuel filter and your return line, it can't vapor lock up there (past pump) as the (boiling fuel) pressure is going to be vented to the tank via the 1/4 return line (and possible overcome that 9.5 psi issue) . If the fuel is boiling in the supply line it will expand and force itself out the tank end as there is less resistance in that direction. then youll have a dry line, no pump output pressure and carb bowls that are empty. Worth a shot to shield or wrap those fuel lines where they pass a hot surface if not already shielded.