Bump with some added info and comments.
I have no clue on twist, Bushy website doesnt address it, it only says this is chrome bore and barrel. The barrel is not lightweight or turned down. It was bought by me as a Dissipator Factory upper complete NIW and I had the rail installed.
I have no clue whose rail that is. The guy had it, I wanted one, he installed it in his shop and returned my spare parts. Its solid and secure and worked well. Everything lined up. Im really surprised someone hasnt chimed in and said who made it, I'm sure its not a one of a kind.
I bought it new and barely shot it, the only detraction on it is the surface scratches. It hasnt been abused in any way, and is just barely at the Bushmaster standard of "broke in".
Bushmaster sells a NIW Dissipator upper minus B/BC/CH for $395. This is exactly that, plus the rail.