Plumbing your mechanical fuel pump (Surge tank in the front (recommended) Plumbing from the lift pump in the main tank is Oem line of -6 from the main tank lift to the surge in the front of the car though a 100 micron filter 320- x 460 is HEAPS as they flow near double when not under pressure.
-10 line, up to 700 pumps, -12 from 800 - 1100, -16 1300- 1600 pumps, from bottom of surge to inlet of fuel pump Outlet of pump to fuel filter 10 micron, to injector rail, or at least filter before regulator.
-8 to fuel rails (or -10 if its a big system 1500 hp plus) then continue the same back to the surge Then from surge to main tank, preferably -10 so you can vent the tank and not build vacuum when the mech pump is pulling more than the lift can supply. (-8 MIN). Surge tanks in the back of the car Larger surge recommended, the higher the better unless you run a prime pump then it does not matter. Run a lift pump from main tank to the surge (oem line, -6 whatever) lift pump can be OEM or walbro 320 not crucial but will impact on the size of the surge as you don’t want to run out of fuel in the surge.
By calculation you work out the engines fuel consumption per minute and divide by 6, that gives you 10 seconds at full throttle (more than you will ever be on full throttle without getting off it) Then you run 2 x -10 lines from the bottom of the surge, 1 goes to the main pump (mech pump) the other comes out of the surge into an inline pump (044 for eg) then through a high flow check valve and tee it into the main supply line. (-10 line, up to 700 pumps, -12 from 800 - 1100, -16 1300- 1600 pumps. from bottom of surge to inlet of fuel pump) The main supply line needs a check valve before the prime line tees in, and a 100 micron filter after the prime line tees in but before the pump.
Then from the pump, you run your 10 micron filter to protect the injectors and reg (at least the reg) can all be -8 for series 1 tough pumps and -10 for series 2 pumps. The reg then returns to the surge like any other fuel system. Vent the surge to the main tank with as large a vent as possible (-10 works well) this will allow the return from surge to main to also allow air to pass through the line to avoid a vacuum in the surge which is not ideal.