I don’t have the schematic you have to look at but I can assure you that the ignition wiring for XR7 and standard both use a resistance wire. Typically it is shown adjacent to the key switch (standard) or just after the tach (XR-7) in the schematic. I think this may all be moot though as your car is so highly modified that I think you are just going to have to go by what you find. What you see on the schematic is maybe an idea of how it once was wired but probably all that has changed to such a degree it may add more confusion that any thing else.
There is a resistor wire that goes to the coil (16A) but it’s not in the 904 circuit. I’ve attached the schematic I have of a 1969 Cougar XR7.
The mods I made don’t effect the 904 wire from the ignition.
I tried to send you the schematic I have, but for some reason the site isn’t accepting attachments.
I use the “69 Cougar Wiring Diagram Manual” that you can get at WWCC. The Page is “1969 Cougar XR7 Ignition, Starting, Charging, Gauges, Convenience Prove-Out And Tachometer”.
If you look at the standard cougar schematic the 904 circuit clearly shows a resistor wire in the circuit, the XR7 schematic has no resistor in the 904 circuit.