Well, I talked to Kevin at Vans Builder Support this morning, and the gist of the conversation was that I was trying to solve for a problem that doesn't exist. i.e. the engineering is correct, and that teeny rivet pitch above the start contactor is per Engineering.
The 3 most obvious choices are 1-build per print, 2- skip the nutplate and just use a fiber lock nut on the cabin side, 3- lower the contactor enough to drill the next lower rivet hole 0.25 for a bolt and then center the nutplate on that. Kevin confirmed that any of those options are fine.
I originally though I would go with option 2, but the more I thought about how much it would suck to be stuck on the road somewhere and not be able to swap out this $15 part without a second person, the more I didn't like that idea. Eventually I went with Vans engineering. you may be able to see in the photo, but I went with an oops rivet in this location just for convenience of not having to countersink the firewall so deep.
Turns out that when I got to looking this, the starboard most nutplate for the BATT contactor has the same thing going on, as does the fuel line doubler (just with rivet, not a nutplate)
Long story short, I installed the contactor nut plates per print, but elected to make the fuel doubler 5/8" taller which allowed me to pick up a second existing rivet in the firewall & vertical member rather than having yet another rivet with ridiculously small pitch. I also made it about 3/8 wider. These two things allowed me to move the fuel fitting penetration both laterally and vertically about 3/8" to relieve the otherwise uncomfortably close proximity to the hot lug of the start contactor that everybody warns you about.
Like a lot of things on this project, this seemed like such a simple operation, but ended up taking way more time than expected.
Anyway, it's all done now and came out okay