Yep, they're Nikasil plated. The original barrels were well-worn and smooth. I had the choice of boring to 1st over, getting the 1000cc Siebenrock kit, or Nik plating. I had a conversation with my Airhead mechanic about it. His take was that a 1st over bore is basically just buying time. The new bore wouldn't last as long as the original, and the work + new pistons would be costly. He wasn't a fan of the Siebenrock kit, so he advised Nikasil plating.
If dino gearbox oil doesn't do much to help, the plan is to pull the transmission, remove the rear cover, re-clean the mating surfaces, and place the cover against a granite machinist's plate to see if there's any discernible warping. If it is warped, well, I guess I'm screwed.
I may have the longer top hat spacer from my /6 parts bike. I'll take a peek tonight. I have a big tube swing arm at the powder coater's, so once that's done it's going on the bike anyway.