I agree that it has some similarities to known DCM alterations, but still one real conflict.

Regardless of the wood overhang - or the distance from tip to muzzle - we appear to have a "problem" - i.e., a rifle-style forend (band-retention) treatment, with (apparently, unless I read it wrong) no butt swivel mortise. That animal does not exist in nature.

No clue as to "no cutoff"; it surely had one when it left SA, unless we are talking about a lunchbox special.

Also, do not ignore the possibility of a completely hand-made stock - I've actually seen such a beast, damndest thing you ever saw. Real head-scratcher at first.