I'm looking at the current auction number 7386090422 on ebay for a 1981 Series II 12-string. I've never tried one of these live, but I remember seeing music videos in the 80's of Triumph using one of these (I think). My understanding is that Alembic single coils have a different kind of range of sound than conventional single coils. If that's correct can someone tell me about them?  I understand that they're hum canceling with the dummy pickup and all (right?), but would I have to sacrifice a fat humbucking sound entirely?

I don't think you'll be sacrificing much of anything with a series II!! The filters (one for each pickup) will make the pickups sound most anyway you like. IMHO, it is the most versitile tone modifying circuit ever designed!