Lots of cars came without a vapor return line. The vapor return line has advantages. I think one is that it keeps the fuel supplied to the carb slightly cooler.
The strongest mechanical pumps I know of are the RobbMc brand. One of these, along with 1/2" line back to the tank should supply your engine. They are available with a vapor return option. "...Bottom "Vapor Return" Port: 1/8 NPT (metered)..."
I ran all my 455 bracket cars with factory 3/8 line from the tank, a stock mechanical pump, with a Carter P4070 elec "pusher" pump back near the tank. Only switched the elec pump on for a pass down the track.The mechanical will pull thru the Carter elec pump, for normal driving. This system worked OK down into the high 11's. My home built 455's probably had around 400hp/500 torque.
The Carter P4602RV elec pump is said to have a bypass fuel line, to make it easier for the mechanical pump to pull fuel, when the elec pump is not turned on.
"...I needed an electric fuel pump to act as a primer and booster pump to work with my performance mechanical pump. This pump was exactly what I needed and it comes with a bypass and check valve, plus it is made in the USA..."
