Not to sound like a broken record but......I've had the same vapor lock symptoms since we switched over to E10 fuel. I tried both an electric pump as a primary source and also in series with the mechanical pump.
After shutting the engine down (without opening the hood) it would crank and run until the bowls in my C/W's emptied and then it would die. My fuel pressure gauge, which normally reads 4-1/2psi would read zero. The electric pump both as the primary source and also as a supplimental pump made no difference. The problem is that E10 fuel has a "phase seperation" point of about 128 degrees.....and the engine compartment reaches well above that within minutes of shutting down.
In duplicating the problem I discovered that a wet rag laid on the metal fuel line right at the corner of the valve cover, where the line starts back to the carbs, immediately restored fuel pressure. I tried insulating the line between the valve cover and the thermostat housing to no avail. At this point I switched back to the mechanical pump as the primary source of pressure.
The process to correct the problem has had me fabricating an aluminum heat shield that I thought might deflect enough of the heat soak to correct the problem. It didn't. Popping the hood after shutting down the engine allows enough heat to escape so that the problem corrects itself in 15-20 minutes. I've also resorted to running my supplimental a/c pusher fan for 5 minutes after shutting down which seems to work okay. I have a strong hunch that my creative metal fuel line setup is a major contributing factor but I never once had this problem until my first tank of E10 fuel after a year and a half of driving. (a full tank a week) My next corrective action attempt will be to change out the metal line to E10 rated rubber hose and see if I can't reduce the 150 degree temperature, after shutdown, in the metal line.
Before you invest in an electric pump try applying a wet rag to the line that runs up from the pump to the carbs. If you're experiencing the same issues as mine your engine should pick back up and run normally. I'll also add that the "wet rag" has proven to be a quick fix at several of our shows where a vehicle drove in just fine, and wouldn't run after their float bowl emptied. If allowed to cool down, the vehicle will start and run fine but will repeat the process if allowed to sit after shutting down for a short period of time.
I'm not saying that your issue is the same as mine but adding an electric pump didn't correct my situation.
Dave
