All the British sighting telescopes are dimensionally interchangeable. The main differences, other than the graticules which are type specific are magnification, (either x1.9 or x3), lit graticule or not, (the L after the x3 in the picture) and fixed or moving graticule, the example shown being fixed. The moving graticules require a larger head diameter and have two adjusting knobs.
The x1.9 for tanks are for the front machine gun but also have the main armament range scales so they can be used in an emergency, the correct turret telescope having the x3 magnification. There is also a x6 eyepiece which fits in place of the rear lens though with a 75mm, that would only be of use for HE!