Go to the u pull it yard and get the complete dura spark 2 system off of a 76-77 ish 5.0 . The dizzy will have the vacuum can and the module will have a blue grommet. Get the coil and bracket too.Look the harness over well, most of the duraspark is pretty easy to see. The only place you should need to clip it will be at the red wire for the power from the ignition, clip it on the side closest to the ignition switch( keeping the connector intact) as you will need the white wire to hook to the starter solenoid for the Ignition bypass(during starting).
You can power it with the output from the EEC 4 relay and from the correct starter solenoid.
If you are running a msd then follow there instructions using the output wire from the EEC 4 relay (blue w/red) for the white wire on the msd box (ignition switch on/off circuit)
Sounds like you have a fuel pump on the motor so ignore fule pump wiring , change the sending unit to a non efi sender to eliminate the fuel pump being there as it can cause a starvation problem.