That lip that you have circled in red is all that goes into the stock. You really don't need to tap the screws in, the tolerance is so close that they will begin to screw into the stock. Insert them into the backing plate, place the plate on the opposite side of the stock and begin screwing them in till you feel them begin to protude. Position the qd so that one hole aligns up with a screw, tighten a couple turns then align the second hole with the other screw and tighten a couple turns. Alternate tightening each screw so that the qd is pulled evenly till tight.