Good post, Doug---
I'm still not quite over my more 'precise' gunmaking life, but I'm working on it.
My old business partner, Brian, would say, "We ain't buildin' no damn piano!"
There's a certain amount of 'self fitting' in any machinery. You're right, electric motors are a different animal entirely, so are jet turbines gyroscopic friction drives, but engines have a certain amount of 'running clearance' that develops as the roughness wears off.
In my *opinion*, after hatching two of them and watching one grow old and retire-- It's better to clean it out, grease it good, and crank it up. Run it 50 hours or so and LOOK at it, and listen to it, ring it, and rub the goo out of the trash catcher between your fingers and determine if there's a canibal hiding in the engine somewhere. If the answer is 'no', run it some more. Put a thousand hours on it and then take it apart and see if something NEEDS doing.
If a cam turns freely and doesn't rattle there's no reason to drive out bushings looking for trouble...yet. It'll let you know without flinging parts in the neighbor's yard. SLOW speed means there's time to identify what *might* be going wrong before it makes smoke, sparks, expensive noises, and adrenalin squirts.
I'm just suggesting figuring out what's wrong with it by running it instead of worrying about it.
Remember, it's only beurocrats and polititians that *fix* things that don't need it.