yes bowman jig didn't come with the round bar, at least not when I got my jig from him.Bowman arms has a jig with one , i think 2 active on GB.
As for the dimension you seek , is it for the rear de-milled portion? Why not measure the round piece that goes to the gun and go a CH bigger? You know, the round piece with the 2 slots for the stock?
(Oh, GB = Gun Broker, CH = **** Hair, an official unit of measure)