Good Method to Add Wiring For Add-Ons

I'm not going to be a lot of help right now, but the thing to test is whether relay will work close at say 9 volts when starting.
The line lock doesn't matter, but the fuel pump might matter depending on how much fuel is in the bowl.
160 mA @ 13.8VDC is pretty low. Lets say you use the run wire to trigger it. During start the battery gets drawn down to 10 or 11 Volts.
With the relay on the run side of the ballast resistor, there will be no more than .16 Amps going through the resistor.
change in V=I x R
change in V = .16 Amps x .5 ohms
change in V = .08 Volts.
So the relay will be powered by only a tenth of volt less than battery voltage during starting. So as far as that goes, ignition run circuit is probably OK.
Piggyback onto the ballast resistor or maybe there is an unused terminal from some feature on a '74 that you're not using. Choke assist? Idle stop solenoid, that sort of thing if you got rid of them.