The difference is obvious if you have one in hand...it actually is stamped MC 5D. M's have this stock too, so the unless the seller is like us...google will show them an M first. They don't notice pesky things like the mag release.
I kinda want one, but the only one I have seen locally was seven years ago at a gun show. The seller was some 80 year old cowboy type, with nothing but six shooters and holsters...and this MC-5D outfitted with the brightest clamp on green laser I have ever seen. He turned it on, and was waving it with a 30 rounder hanging out....totally freaking out the post Sandy Hook wives in tote across the entire building.
He only wanted $895 for it.
I didn't have the heart to tell him the mag wasn't right for the gun, and instead left him to be glared at without me being an accomplice.
About two minutes later I was scoffing at a NIB Thumbhole sporter at $550
I have not seen a commercial SKS for sale around here....anywhere since.
With this guy, bring a laptop, show him it's not a D, but an M...and haggle it down...especially if he doesn't have the five rounder. But block access to Gunbroker first.