I believe - and I cannot say this for sure - that Len's reference was to the feeding device being "large capacity" and not the rifle itself. Again I say that from a post I read here, not any sort of intimate knowledge of the case, or anything along those lines... so I could very well be completely wrong.
The text of the AWB, 18 USC 921(a)(30), reads "a semiautomatic rifle that has an ability to accept a detachable magazine and..." which leads me to believe that a prosecutor could successfully argue that any SKS is covered. Obviously ANY rifle could be modified to accept a detachable magazine with enough work, even a tube-fed or single-shot, but with the SKS you simply remove the "fixed" magazine and replace it with a detachable, without using any tools or making any modifications so to speak.
Keep in mind there are "assault weapons" and there are "large capacity rifles" in MA law. They are not the same thing; the latter would not be an AWB issue, but would present an issue for an FID holder (as opposed to an LTC holder).
Regardless, the '94/'98 AWB refers to possession, not manufacture. A pistol or rifle cannot be "preban" if it was not in the US on September 13th of 1994 - which many/most Yugo SKS were not. Obviously all Chinese SKS came in before the AWB date (and only have one "evil" feature anyway, the bayo lug). Loads of Russians came in before '94 and similarly have only the one offending feature - and they're not coming in currently. All of the 20 or so Yugo SKS I ran into at Cabela's were recent imports, and Yugos all have a grenade launcher and a bayonet, some even have a flash hider built into the grenade launcher.