Unsigned relic, usually attributed to Neihart as Ed noted above. Paul, you can see the 'break' lines along the comb that delineate the comb, and you can see how the upper portion of the buttplate sets the width at the comb then tapers inward faster than the comb itself. Viewed from the side however, it generally looks continuous (i.e., the upper portion of the comb and buttplate should be a continuous arc). This one is somewhat unique as you can still see how the three flats of the buttplate return were actually carried into the comb for some distance. Very difficult to photograph but "in hand" it is fairly evident.
I always have found these buttplates easiest to inlet when the butt is shaped out fairly closely to finished form *before* installing buttplate. The rear (shoulder portion) of the butt is cut fairly closely to the buttplate curvature, butt shaped out, then buttplate inlet down and forward carefully. You can then just lightly hammer the shoulder portion (which should be thin and malleable anyway) to final fit. There should be fairly heavy bevels on the upper side edges so that the small strips of wood along the side, when final shaped, taper rapidly thicker toward the inside bottom and so retain strength (so they don't break out, especially back near the curve).
