First off, that is one beautiful M&P Target, and having a birth year gun is always a special kick. M&P Targets are a favorite of mine, only have one with a humpback hammer.
The grips on paplinkers gun are original Ropers, and a rather unique set made with an integral trigger stop built into the left panel. Was not a particularly great idea but Walter Roper has to be credited with trying new things.
Keith certainly is an authority!
Not to thread drift but here is the other side

I have two Sanderson sets that have this feature also