Will,
Very interesting thread, thanks for sharing. I've got two of these plates kicking around , one with some test holes drilled into it, though in my case I was thinking of a mill at the time.
Regarding long bolts loosening over time, it could happen due to different thermal growths of the materials if the machine is somewhere it will thermal cycle a lot, such as an uninsulated shop/garage. Loctite or locknuts should be cheap insurance against that.
Regards,
Raymond