Joe, The wood alongside the selector has to be slightly hollowed out to let the selector slide move freely side to side.
I converted a two trigger stock to accept a HOT and used my mortising machine that I use for wood working, and used a Foredom like tool but faster, Cyclone, to make the hollows on each side of the selector, using a ball shaped burr.
Back when Hunter did this work, you would send them the gun and for $25.00 they would install a HOT, same price if you ordered it with the gun.
In a Sept. 15, 1948 Repair Price list from the now L.C. Smith Gun Co. (Marlin), this same job cost $45.00.
