Marc,
The adapter, complete in its box, is $ 125, +/- as I recall.
The feel is unlike any type of target stocks, Kearsarge, Roper, Sanderson, etc.
These adapters do two things: First, the two steel plates make the grip thicker.
Second, the rubber pad 'lifts' the muzzle of the gun up, giving the target-shooter a 'natural' aiming position.
I understand that Elmer Keith was a S&W grip adapter fan, 'back in the day'.
Some shooters milled their Magna stocks to accept the grip adapters, and the combination of the longer Magna stocks
and the grip adapter gave a 'feel' more similar to a modern target stock.
Below is a picture of S&W Registered
Magnum #3447.
It was a test-and-evaluation gun for S&W, manufactured in 1938.
It was also a 'loaner' to certain shooters of that era.
The Magnas were milled by the factory to accommodate the grip adapter.
Shooting position, feel and accuracy are fantastic with this setup.
The micro-click rear sight was added by the factory as one of the very first of its kind, and in 1946 the gun was sent to the Westfield, MA Police Dept for their evaluation.
The humpback hammer is original to the gun.
The grip adapter is an original.
Don