[b]AK Fan[/b], bottom line here:
The 1989 ban only applies to IMPORTED "assault"-type weapons. The AK-47 was affected, as it's imported. The AR-15 wasn't affected because it isn't imported. No worries with the Bush ban for you! [:D]
If it's missing the bayo lug but still has a collapsable stock or flash hider, it's still a preban. Around the time Bush passed his ban, Colt got worried and "sporterized" their rifles by removing the bayo lug. It means nothing; you can go ahead and stick on an upper with a bayo lug if you so desire.
The 1994 ban is what you need to watch. Does that AR-15 have a collapsable stock, flash suppressor, or bayonet lug? If so, it had to be a [i]complete rifle[/i] [u]before[/u] September 13, 1994. If it was made after that date or wasn't a complete rifle before that date you can't have the collaosable stock, bayo lug, or flash suppressor.
My advice is to view the above serial number list AND call the manufacturer to confirm the pre/post ban status.
Good luck!
Mike