Is the groove that is machined in the top strap of an adjustable sighted K frame revolver the same dimensions as the groove/rear sight channel on a fixed sight piece? In other words, could one simply install an adjustable sight on a fixed sight frame by drilling and tapping for the mounting screws? I know the front sight would have to change.

Just curious and don't want to pull the sights off of any of mine to take measurements.

Simply, no. The top strap is completely different.