I made a rear bar to replace a broken MiniSpares one - no problem with the MS bar as such, but my diligent and persistent lack of maintenance caused the joints to seize up and break a blade off the bar. I used a solid 12mm (1/2") bar and 3mm blades, and "green" pipe clamps to hold the bar to the subframe like the KAD bar does.
Took it off the car two years ago and now I can't find the drop links or pipe clamps...........
I did have a roll-bar calculation tool at one time, comparing stiffness of solid vs hollow etc. I could see if I could find it again it you're interested.
Phil.
Edited to add : See if you can find pictures of some Miglia's, they use all sorts of arrangements. Most seem to be mounted in the boot on a hard point such as a rear turret strut "brace" with long drop-links through the floor onto either the damper bolt or some arrangement on the rear brake backplate.
Edited by phil hill, 17 November 2014 - 04:34 PM.