Ok, I did a little work with photoshop with two pre-ban M4 uppers, placing them side by side, lined up by the tip of the barrels, and the bayo lug on the 14.5" barrel lines up where the adapter needs to be on the 16" M4 barrel.
My conclusion from what I saw was, mounting this adapter on the thicker part of the barrel in front of the front sight post and right before the 203 notch, will put the lug in the exact same position (in reference to the end of the barrel & the A2 birdcage) as it is on the real 14.5" M4 profile barrels (which supostedly is the correct combination for using a M7/M8/M9 bayonet).
I guess all thats left to figure out is the barrel diameter on the M4 barrels where it meets the front sight post. Any ideas? (0.75 or 0.57)? I'm guessing it's probably 0.75.