I'm going to use this resin putty to build up the routed out area to what it 'Should' have been, then install the binding as originally intended.
Mask off the binding and spray it Black.
So the end result should look something like the rear of a 50's Gibson super 400 headstock, but I might bling that up a bit with a Art Deco design in that Gold paint
I'll taper it down the rear of the headstock, after I Blonde shellac the neck to bring out the grain, then run a black stripe down the center, into a reverse Black area of the neck heel, similar to this.
I haven't decided on the Gold design motif yet, as my attention has been spent trying to salvage this build because of my blunder.