A further followup.
We had our only race of the year at the beginning of the month.
The engine had significant blow by issues from the moment we unloaded it off the trailer, we must have damaged a ring while tuning. When we tear it down we'll know for sure.
After driving for a bit we started having misfires so I pulled the plugs and checked them, and they looked fine.
I swapped in the iridium plugs as a test and the car ran much better. ¯\_(ツ)_/¯
After a short while on the track we had a catastrophic wheel bearing failure that snapped the axle and let the wheel escape.
It broke the brake caliper bracket on its way out and since it's rare and we had no spares our race was over.
Here's some in car video from the race: https://www.youtube.com/watch?v=SCmnJtaC9RY