Fellow Enthusiasts,
I am shopping for my first drilling and have decided it must have a scope
The most common mounting system is the claw mount. As you pointed out they are all custom. If the drilling does not have a scope you will need to have the rings fitted to the bases and in some cases you might have to replace the bases. This will run $600 to $1200 plus the scope.
I have found the best scopes are from the drilling made during the commie period specifically from 1960-1989 and my prefered city is Suhl. My Fortuna, Merkel and Wolf all from this time frame all have excellent Zeiss scopes.
You might want to search for a drilling with a Zeiss scope.
Given this is your first drilling have you selected a "drilling smith" to inspect the gun? My first drilling needed a lot of work and the seller was willing to work with me on the price.
Also are you going to expand the shotgun chambers to 2.75 inches and open the chokes? This will run approximately $400
If the gun is off face, that will run approximately $600 to repair.
The 'drilling smith" I use was chosen based on recommendation from a buddy of mine that is very particular about his drilling
Good luck in your first drilling purchase.
Doug