You might look into the Two Wire mod. Hesitated to mention it at first due to the condition of your harness. First, need to see if you get voltage at the JB plug when the start button is pushed.
Sorry, I don't have wire colors and pin numbers right now.
Replacing a harness isn't too bad, each plug will only fit in one place, except for a couple of bullet connectors toward the front. It has been posted, there's a slight variance between years, but easily dealt with.
Can't help but notice that this method does not provide voltage on pin 2 of the ignition coil ignitor (red/white wire). I don't doubt that your suggested setup works, but does anyone know what the ignitor box does with that input from the start button?
If you're referring to the small gauge wire on the spade terminal of the solenoid .... Isn't that the start button circuit from the JB?
I don't know of any other wiring coming off the starter solenoid.
Now .. Back toward the start button, before that wire reaches the JB, there's a wire that branches to the IC Ignitor box. That branching wire has remained a mystery, though some of us suspect it may alter timing as the start button is pushed. (branches off the start circuit) We discussed it some in the Two Wire Mod thread.
The starter button I described will only serve to activate the starter.
All this reminds me that I never put those updated pics into post #1 at the Two Wire mod thread.