The 10ga frame is an SB2 shotgun frame, same investment cast, heat treated alloy steel as the SB2 rifle frame, same external dimensions, but the frame sides are thinner at the top for the much larger 10ga(and 12ga USH) chamber swells, 1.2" in diameter as compared to 1.1" for all the other H&R barrels. All H&R stocks fit it just like any SB1 or SB2 rifle frame, but the forends have a much bigger barrel channel since they're bigger in diameter.
Tim