[Linked Image from i.imgur.com]

My reprint of a 1900’s Holland and Holland catalogue seems to have gone into hiding, so here is the same illustration from Wal Winfer’s book.

Your rifle differs in having the locking catch recess on the rear base, but the principle is the same. You put the scope on by sliding it backwards on to the dovetails until it meets the stops, and then the swing over lever rolls the catch in to the groove on the base to stop it moving forward on recoil.

If you can find a suitable Voightlander Skopar sight and are having mounts machined to fit the bases, why not at the same time have a second set made in which you can mount a straight tube 1 to 5 or thereabouts good quality modern scope mounted as low as you can without fouling the top lever, doing away with the peep holes for the open sights.

That would minimise differences in cheek weld. If the rifle was ordered for a scope to be fitted, Holland’s stocker probably incorporated some degree of compromise in the comb height.