Sharing this in case it helps others. Inspection of the car during the first shakedown event showed a lot of the suspension bolts were loosening. This is mostly normal for a fresh build, usually things need to be re-torqued at least once before they will stay put. The problem areas were anywhere that had powdercoat on the surface that the bolt/nut mated with. Those kept loosening. This is due to the powdercoating having some squish to it. Back at the shop after the first event I added a traditional split lock washer to every nut/bolt that went in to a powdercoated surface because the lock washer can dig through the coating. Also added blue loctite to just about everything in suspension and brakes. That did the trick everywhere but in one place: the nut on the Rear/Lower/Outer long bolt in the control arm still kept loosening. I'm running spherical bearings in all factory bushing locations, but I'm unsure if this is related.

This nut needed to be fixed for good, but still serviceable. Nowhere nearby to easily safety-wire it to. Here was the solution:

Factory NB long bolt (NA bolt won't work because it's coarse thread): 9YA1-01-201
Factory castle nut for a steering tie rod end: 9992-41-201
(I ended up not using the factory cotter pins in the pic, went with ones that were just a bit thinner)



Drill the bolt ends and voila:

 

Looks like the part number worked

 

I struggle with keeping those tight even on non-PC'd arms. SOP is 100+ft.lbs into them and check them regularly. This is a much better solution.