If you want as close as possible to the real deal. Go with COLT.
There are some guys on the website who are taking orders for after Sept.14.
Colt I believe has a taller FSB which Bushmaster doesn't, the taller FSB helps with the shorter sight radius.
You can order one with a Perm. attached phantom/vortex to a 14.5" bbl. which gives an overall length of 16.1".
Go with that, I wouldnt go with the 16" bbl with A2 FH because it extends over 17" why not get a 20" if you are going to do that, not to mention you couldnt use the bayonet if you wanted to, it would look stupid or you would need an extension for the bayonet. Basically it would be like tits on a boar, not much use ehh.
With a 14.5" perm. attached Phantom you can use the bayonet lug and it will still be a twat hair over the required 16".