I am pretty sure that I am using the KA version, which in that case, no, there is no threading. Mind you, if you loose the front-end (front barrel, gas block) there is threading, just the silencer will be sunken to the fore-grip.
Just looking at Huangs post there, his version has a longer front barrel, by around ~2-4 inches I would guess. Mine definitely looks a little shorter. Can't hurt to keep safe and get the 510mm but if you want to go the $$$ route, get a bore-up kit, a Modify torque-up gear thingy (it's new, it's hip), nice strong spring, and a Madbull 590mm tightbore.
-Daes