I took the engine to NAMES and ran it a short while before running into a couple of issues. The first was that the gib key was a bit loose allowing the flywheel to work loose after some time. The other was that the grub screw for the eccentric would work loose, obviously causing the operation to stop. As it happens the screw itself was aligned with the crank web afer timing, so I could fasten it again and keep running. I also noticed that the flywheel wasn't running true either.
This morning I removed the crank assembly and added additional grub screws for the crank web and eccentric. There is miniscule clearance in the bearing that still allows a bit of wobble when viewing the flywheel rim, but it's much closer to true.