No maching required.
Just remove the two top screws as you would during disassembly, and replace the iron sight bar with the appropiate Weaver mount for the Buckmark.
Check the following websites to purchase the Weaver mount: Cabela's, Natchez Shooters, Brownells, Midway Usa, Browning, Weaver, B-square, and Sportsman Warehouse.
I have the current issue of Midway Usa catalog, and the mount is on page512, product #325-241, blued for $27.99. This one is made by B-square.
Weigand also makes one for $29.95 in the same catalog. Blued or stainless.