wiring for EFI

I have a 1970 Duster, 408 with just over 500hp. I’m planning on going efi this winter. I can follow a electric schematic, understand switches and such but that’s about it electrically. The Duster has stock wiring, no modifications. No electric add-ons like electric fans or big thumpin subwoofers, although the efi will required a electric fuel pump. I do have Crackback’s headlight relay kit. I have had pretty much all the wires forward of the front seats apart, cleaned terminals and wires, replaced where I thought it was required. That included the fuse box and the bulkhead connector.

The EFI requires a power source when the key is in both the run and cranking position. Holley can’t give me a definitive power draw, but say it’s only a couple amps. I plan on using my electric choke wire for the run power source. What can I use for when the engine is cranking? Is there a feed off the fuse box that will do both? I think I have seen a thread about using a yellow wire off the starter relay, and also a thread about a brown wire somewhere. If I have a separate run and cranking source, can I just splice them together and run it to the efi, or do I need something so all those electrons don’t go backward through the other wire, if that makes sense.

I also would like to have an shut off to the fuel pump in case of an accident. Can’t use a oil pressure switch as I need to prime the efi and with the engine off, no oil pressure so no pump. I have read about a G switch. Would that be in the main power feed to the pump, or powering the relay. Holley sniper and Fitech both have relays for the fuel pump and I was planning on using those features. Is there a g switch from some other vehicle I can wire on the power supply to the pump?