Everything looks wrong here. To begin with...the CL AD says "I am selling these for a family owned dealership"...immediately injecting a 'middle-man' needed to sell four NOS 660's??...Come on. Might be selling them for a family-owned all-u-can eat Chinese buffet.
There's not a knowledgeable Stihl dealer on this planet who would unbox those things and not start to smell ******** if they were received by them from the factory. Badging, sticker, owners manual, etc...all as mentioned in previous posts just reak of a scam. No doubt in my mind these things came from a factory...a sweatshop in downtown Beijing. I think you'd probably find a better looking knockoff from a shop in Tijuana, lol.
I guess maybe Stihl started using peel and stick 'Stihl' stickers that the owner gets to apply to the clutch cover as well...lol. Funny...I've always seen the Stihl logo molded into the cover. I wouldn't offer this seller $660 for all four of'em.
If these things are the real deal, I'll certainly eat my words no doubt...but something tells me I ain't got nuthin' to worry about there.