The serial is too early for a .22HP so the brl has been replaced.
Only .22HP brl with a Style 3 address would be a featherweight.
I think the brl is set solid as we would see the TD button on the bottom of the forearm and there is no TD hardware at rear of forearm.
I think the butt stock and lever are original and would guess the rifle originally had a rifle weight brl. If correct then the forearm is probably a replacement. The front of the forearm appears to fit the brl well while a rifle weight channel would be more open.
David might be correct on the groove being for a silencer.
Front sight is a replacement. I can't tell the brl or forearm length from the photos.
Can't tell where he is seeing the "170" stamping.