Yeah, sorry about the high jack on the post. Some of is sort of related.
We went through this last year I think, about how they measure hose by ID and steel line by OD. So a steel line that measures 3/8OD is actually 5/16" ID. Where as a 3/8" hose is actually 3/8" ID.

I will just say that on paper maybe the pump should keep up but that's not what I found to be the case. My 400 only runs about 360HP(320at the wheels) and the car would nose dive at the 1000 ft mark with the mechanical pump and it didn't with the electric, no other changes at all. Apparently it was still going lean with the electric but didn't actually run out of fuel entirely before the 1/4mile.
I installed a return line from the fuel pump to the tank and am counting on that to work as my pressure regulator. The elect will supply fuel up to the mech and then, hopefully, the mech pump will be able to keep up with useage. If that doesn't work I may run the return line all the way up to a pressure regulator by the carb and block off the return port on the pump. I heard from plenty of guys that said the stock fuel line was big enough to support 550-600 HP as long as the pump was up to it. No real need to go to a larger supply line.

I'm guessing that RobMc would suggest you buy their pump with the 1/2" pickup. I'm not sure it will accommodate a return line.