Well, my spacers only add up to 7.5 mm. I have 5 mm on the left and 2.5 mm on the right. And that is with everything tightened except the fork caps so the forks were relaxed sitting on the axle and not forced inward or outward.
So the mystery continues! I'll do some browsing and see if I can find another possibility.
One other thing that is different than my CL350 is on the boss that the brake stay bolts to has two reinforcements cast in it.
5mm on left side.
2.5mm on right side.
Unknown wheel with reinforcements.
`69 CL350 wheel