The part of the RSB there is where it would be on a normal build setup. I have the steel pipe going from it to the gasblack, so there is no gap between the RSB section and the trunnion.
Basically, square RSB, round pipe for gastube. Welded all the way around where they meet, to make it one piece with no gaps. the pipe and gas block are not joined, i just fitted the pipe to the proper length so that when the barrel was pressed in, it would mate up like a regular gastube and gasblock would.