I believe that any barrel assembly that Bushmaster offers is available in pre-ban or post-ban configurations. Bushmaster's catalog lists both for the 16" Dissipator (I do not know about the M4 Dissipator).
I was told by BM on this board that the dissiparor was avail. with the m4 bbl in either pre or post-ban config. Getting the bayo lug on a dissipator is useless, given the distance between the bayo lug and the flash suppressor.
"The M1 Rifle is the greatest battle implement ever devised." General George S. Patton Jr.,US Army