...I might even ditch the tonestack that I have altogether for just volume and tone, like a 6G3, although just from hearing them I would like to find a way to allow a healthy amount of balanced low end to come through, and if I end up keeping the tone stack, use the bass control to attenuate a really gentle slope between 300Hz and 700Hz to bring hopefully sweet and smooth high and mid frequencies to the front of the mix...
TL;DR I'm trying to get the good cronch
The thing about the classic AB763 Fender Tone stack is that it causes a LOT of signal loss. That tone stack and the NFB line are 2 of the defining differences between the Blackface era fenders and the earlier tweeds, where the blackface models have the mid scooped tone and much more clean headroom while the tweeds have lots of midrage push, little headroom, and less refined wilder distortion when pushed to overdrive. There are other contributing factors for these qualities as well, but these two things are pretty easy places to make changes to an AB763 circuit that can yield huge results in making it sound different and cronchier
Eliminating the NFB line entirely or increasing the resistance there will cause the amp to breakup sooner and reduce the amount of clean headroom. Most old AB763 models used 820 Ohm resister in the NFB line, you could try different values here but I'd suggest starting with a 1.5K NFB resistor (almost 2X's the old fender standard) and increase from there or cut the line out completely if things still aren't wild and woolly enough for you. Lot's of people online like Rob Robinette (
https://robrobinette.com/AB763_Modifications.htm#3-Way_Negative_Feedback ) have designed NFB switches to give the option of allowing more NFB through to clean things up and refine the sound, or adding NFB resistance or cutting NFB out entirely to allow the amp to break up sooner and make the distortion wilder. Also the .01uf capacitor you have in the NFB line isn't necessary, I'm thinking that might have been an error when you drew the schematic up?
The AB763 tone stack is trickier. You can play with it all you want but in the end it's still a low impedance passive tone stack that can only cut and subtract parts of the signal to shape tone, it can't boost any frequencies. As a result it's a heavy load down on the audio signal so you loose a good bit of volume and gain going through it no matter what. The benefit of that tone stack is that it's easy to get familiar sounding classic American mid scooped tone with though.
Going with a single tone control will allow for much more mid range to come through and you will also have much less signal loss, but you loose the ability to shape the tone as much, and there will be no way to make a mid scoop if you want it.
You could try a James/Baxandall tone stack instead. Still just 2 controls, treble & bass, but you can work them to make a mid scoop or a mid boost and there's not near as much loss as a fender AB763 tone stack. There are other options too, if you haven't downloaded the Duncan's Tone Stack Calculator then I highly recommend you do (
http://www.duncanamps.com/tsc/ ) . You'll be able to see everything I'm talking about in tone stacks and also find out how other tone stacks will effect and shape your signal.
I've attached a quick hand drawn edit on your schematic with a NFB switch, an old Ampeg style James/Baxadall tone stack so you can see what those might look like. Also a few suggested edits in red as well. Please excuse the chicken scratch, hope this helps you consider some of the options
