Cuz, get a stop watch and bucket out and simulate the flow / height / pipe losses (restrictions from fittings and tube) requirements and see what you get from the Walbro.

Work out how much fuel your car needs at full boost / noise, add 30% ? and away you go

If you are plumbing the surge tank return into the normal fuel sytem return you may need to consider a vacuum breaker so it does not drain the surge tank when the car is off? or are you running straight back to the fuel tank up top somewhere?