Yes, copper fuel line is a problem. Many will say they've gotten away with using it, but they did just that.........got away with it. It's especially a problem if the car is laid up for a while as copper is a catalyst for oxidation of the fuel, accelerating varnish formation.

As for your vapor locking, most often it's a matter of the mechanical pump being the culprit. Mounted to the block it acts as a heat sink. It is built to pump liquid not vapor, so if the fuel is heated too much coming to the pump, or in the pump itself, it vapor locks. An electric pump solves this because it is usually mounted to the chassis (or submerged in the tank depending on your configuration) away from engine heat (and hopefully exhaust heat). Also check the routing of your fuel as it passes the exhaust system. If it's too close it will pick up heat enroute to the pump, then the extra heat in the mechanical pump has a head start on hitting the fuel's vapor point, and then if your pump is in marginal condition it gets even worse.