I'm trying to figure out whether it makes sense convert to fuel injection, probably via something like the cheap EFI thread.
The modifications to the intake system all make sense.
What I'm wondering: I'd like to use a slosh tank in the engine compartment that the regulator dumps into, so the electric fuel pump pulls from that, the fuel goes to the injector, excess fuel returns into the slosh tank, and then I can build it with baffles and stuff so I don't have to mess with the main fuel tank, and just draw calm, non-bubble-filled fuel from it to refill the slosh tank.
So how do I set that up? What I was thinking of was using the existing mechanical fuel pump to fill the slosh tank, and then I don't have to run a return line back to the main tank. (This isn't in a Datsun and the car it's in has difficult access to modifying the fuel tank, so it's really hard to put a baffle in, for instance.)
But if the mechanical fuel pump is running uncontrolled it'll overfill the slosh tank. I need something like the float valve/needle to restrict it.
Is there a way to set this up so there's no return to the main tank?
I can think of some ways to do this involving ECU control of the electric fuel pump, so it only pushes in as much fuel as the injector needs and there's no return at all, but that's a big chunk of software and tuning that I don't really want to get into.
I could use the slosh tank as a baffling system to reduce most of the bubbles from the high pressure fuel spraying into it, and then run an unpumped drain line from the bottom of that tank to just dump into the main tank, hoping it won't be sufficiently turbulent to get bubbles in the line going forwards.
(I know the recommendation is "just don't ever go below 1/4 a tank" but I'm not the only driver of this car and am dubious that rule would get followed.)

Any thoughts on how y'all would design this?

If you use a needle and float in the slosh (surge) tank to limit the fuel in and it has a bit of head space (volume above cut off) it shouldn't over flow. Your high pressure pump is just a circuit, even if the injectors are off it can't return more fuel than it's drawn out. The tank will still need a breather and depending on application that may need to plump into the emissions control circuit for fuel vapor whether it's a vent like on my 1200 or a charcoal canister or something else.

The other thing I've done is use a lift pump and a liquid level switch so it only pumps when the tank needs filling. This is useful if you've run out of fuel, you can fill the surge tank before turning the motor over.

Hope this helps.

That helps a bunch: thanks! And yeah I was thinking the top of the slosh tank would have a vent and be pumped down probably by manifold vacuum to capture any gas fumes. (I know you have to rigorously account for all the air going into the system to keep the AFR balanced.)