Ok,  everyone hates oly lowers but the one I've got has been great.  If the AWB does go Bye Bye I would like to put a new upper on it with a flash sup.  

The upper I have on it now was hand picked to get a snug fit (it's not an oly upper).  If I were to order a bushmaster upper for my lower what are the chances that it would also have a tight fit??  If it doesn't is it bad?

Are you looking to build your own upper, or just buy an assembled one?  If I were you, I would buy a new barrel, and stay with the upper that I already had.  Rebarreling is simple, and it doesn't take much in the way of tools.

Just responding to your comment about people not liking Oly lowers.  I think they are great.  Not any worse that Bushy, Armalite, etc.  As long as the lower is forged and not cast, it will be fine.

Wes

You could have your existing barrel threaded for a FS.  You could also send your upper to Bushy for them to do a barrel swap if you don't feel comfortable swapping it yourself.  As long as you buy the itme you want installed from Bushmaster, they will install it and do any necessary smithing for free.

BTW, I also think Olympic lowers are pretty good these days.  They have come a long way in the past three or four years.