Use stock 5/16 line for return and ordered stock 3/8 fuel line. regulator at the carb.
For the record, i ran a carter elec. pusher to a carter mechanical pump for many years.
The reason why was the vapor lock problem that the pusher fixed.
Never had a diaphragm failure in 5 or six year... but had a regulator that only allowed the electric pump, to push a couple of pounds, to the mechanical pump. still if it had ruptured, i would probably not figured it out early enough to save my bearings.
It was a risk!
