I have one question, since it is rigid, why make the rear resemble a swingarm?
From an engineering standpoint, it would have been quite a bit stronger if the upper tubes on the rear link would have anchored to the top frame tubes at the same location as the rear sub frame.
As it stands now, looks to me like under high stress it will try to hinge at the current upper link mount which will create a stress (eventual break) point between the upper and lower frame rails.
I see you have a gusset for the sub frame but I don't see any gussets for the rear arm to the frame.
Just my opinion, allthough I must say, the frame is definately a work of art !!!
I must have taken a lot of time to fab that all up. I like the steering set up.
What material did you use, 4130 or DOM, also what wall size ?