I picked up a rather odd upper over the weekend. It is a hbar 20" barrel but has the sight/block set back as you would find on an M-4. It has a 4 point rail system hand guard and it is built on a flat top receiver with a detachable barrel.
I don't care for the barrel length. How difficult would it be to cut back the barrel to 16" and install a "recoil" suppressor?