When my Richmond was still stock with syncronizers I was using a Mcleod Street-Twin and I HATED the way it shifted. I determined one of my problems was the clutch, to much rotating mass to clear for a clean disengagement of the input shaft.
Not sure if you are using that unit but I have seen it in some of your photos. The syncronizers in the street Nash box are the same as a Borg Warner Super T-10 and there are some improved parts out there. There are some road race versions of the syncros that offer improved power shifting. The type of fluid is also an issue when shifting becomes a chore and synthetic is a big no no . I use Passon's gear lube in all my re-builds and my own Richmond box. That Nash is extremely easy to rebuild just don't disassemble the shifter detents they are a pain to re-assemble.
Your firewall wiring looks like mine(very busy) I'm also working on that this winter.
Gus