Tunaman had some center feed classic SS bodies at one point. I think he may still have some. http://www.tunamart.com/index.php?c=20&p=423
Also, I have used L/R TL barrels and just dremeled/drilled slightly indents in to accommodate a CF SS body. As long as your twist lock pin is fairly stiff and you tighten your front frame screw down you really shouldn't have issues with the barrel twisting.