Pulling out one engine and fitting another tonight, found the source of a slight weirdness setting my clutch, the little end insert on mine is drilled off center, you can see it from the end, and when you rotate it in something smooth it's certainly off center.

I'm not sure it effects the clutch in action, though it likely is not great for the trueness of how everything rotates around it, or maybe how it buts against the end of the engine shaft perhaps, not sure how I missed it during the build, weird quality control issue from Mugen.