I use a surge tank set-up on my '68 Barracuda with EFI. The way I have it plumbed is simple and very effective at supplying air free fuel to my injectors even down to the last gallon in my unbaffled tank.

I've never heard of anyone using a needle and seat to control the fuel level in a surge tank. It interesting, but unnecessary. I plumbed mine the more common way by running a feed line from the rear mounted pump and a return line to the tank. No needle and seat is needed, as the fuel simply flows back to the tank with nor restrictions. The surge tank remains full.

I used 3/8 feed and return lines flowing through a pair of Permacool filters/water traps. A stock tank with a silver soldered upsized 3/8 return line in the pick-up, and a small electric fuel pump mounted outside the tank. I could just as easily have used an in tank pump.

The fuel circulates through the lines until it fills the surge tank and then returns to the tank all at nearly "0" psi, as there are no restrictions to this fuel circuit. If the in-tank pick-up does get uncovered while driving with low fuel levels, the air bubble that causes is quickly pumped through the system and purged back into the tank.

Air floats to the top of the surge tank, obviously, and is quickly eliminated from the surge tank. My high pressure fuel pump is mounted inside the surge tank never see's the bubble.

As long as your fuel circuit from the tank to the surge tank has no restrictions, and the feed to your mechanical pump has a pick-up tube located near the bottom of the fuel tank, you should have good results.

The high volume of near 0 psi fuel flowing through the surge tank and fuel circuit keeps the electric pump cool and is very easy on the pump.