i've passed this link on to you already, yes?
sheridan p-series to k-series conversion thoughts...
the 'mounting lug' is the 1/4"-20 screw, washer, and rod coupling/nut that the stock screw screws into...usually they are installed in the p-series in place of the nutsert for the front trigger frame screw, requiring a new hole to be drilled in the stock...