Hi,
To put your mind at rest the spindle hole in the sliders is not bored at 90 degrees. See attached images, the angle I have been told is 89 degrees (thank-you, John Phelan).
I was going to buy a set with a shallow counter-bore but was told the normal fork sliders were also used on some "A" group twins before the change (97-3641 & 97-3645, 1969 and before shown in the attached images and 97-3933 & 97-3934, 1969 and after, shown in your images). So I won't be changing mine, saving some cash for other projects.
This angle will bring the sliders inline when the wheel is fitted. No need to add shims or alter the arrangement, it is as BSA intended. It also tilts the fork slider brake lug into the brake plate.
The poor chap in the photos actually machind his sliders to 90 degrees and fitted caps of equal length.
Best wishes...