I've been offered to trade an Aimpoint ML2 for a preban Colt HBAR 20" A2 upper w/A2 flash suppressor - without the bolt and carrier.  Is that a good/fair deal?  I'd appreciate your opinions.  

So your really just getting an upper and barrel? How sure are you that its colt? And even if it is why do you care?

Good points FNG.  Don't really care that it's Colt.  I've been more than satisfied with Bushmaster's quality.  I haven't tried any other company, but I'm sure some other companies such as RRA, or DPMS would be a decent choice as well.  

I have to look at the facts of what I want.  I'd like a 20" upper with a 1/7" twist and a flat top receiver.  Don't know how common 1/7 twist barrels are.  I'm sure they may pop up in the EE from time to time.  I think I'll hang onto the ML2, put together an 20" upper to swap with my postban AR15E2S, and put my preban lower in the safe and hope the ban goes away next year.  Thanks FNG.