So to recap, ordered this aluminum mount off eBay for $6ish ...
It arrived yesterday ... missing a screw!

Looks like it was boxed like that in the Chinese factory ... threads on that side weren't quite finished either. Got my money refunded. If you get one, use another seller ... plenty about.
So I went into my machine screw bin and found something that would fit ... wrapped some cut bicycle innertube around the engine guard to fit the diameter of the mount, and mounted like so ... it's a little farther away from the cylinder head with better cooler airflow around it, so the camera doesn't get as warm.
Here are the results ... I think the pile of innertube is allowing too much vertical vibration at certain RPMs and road conditions ...
So I dug into my expansive bicycle parts bin to find an old reflector handlebar mount with a firmer rubber sleeve ... cut off the reflector mount screw interface tabs so it would fit under the aluminum mount ... will test it this weekend ...
One thing I'll warn about this aluminum mount ... the threads are aluminum too, not steel, so looks like overtorquing can strip them easily (if I haven't already) ... also noticed they loosened a bit after a 70-mile run, so loctite would be in order.