Looking at the video I'm not surprised you are freaked out Goodlad? Do you know anyone with a 650? try the brace on his/hers?
Cosmo must have some drawings/plans of dimensions for his braces?
To me the most likely explanation is that the lad has sent you the wrong brace! Ie made with the wrong tolerances? Mistake in input on his lathes?
Can anyone with a micrometer and a 650 measure the top of their fork leg? Goodlad do the same, see if they match?