I fabbed a 6 pt out of 1-3/4 chrome moly with fixed door bars and rear x-brace. I intend to make it a full cage and redo the side bars as double bars.
I highly (and I mean highly) recommend that you go custom fabrication from a race shop if you want a full cage. Expect to pay $2000-4000. The issue is that on a C5 that 1-3/4" tube running directly next
to the left side of your head (above the window that connects from hoop to rear hoop) will damn near kill you if you are hit on the left even with padding unless you are wearing a helmet at the time.
Go out to your car and sit in the driver seat, and take a look and you'll see how close it is already to your head... without the bar.
Anything but a cage custom made
inside your car will put the top "above-window" bar even closer
to your skull. The gaps will be way less with custom.
Go custom on this safety device, cheap is never right... right is never cheap.
Cages are cool, and look mean, but they can also increase
the likelyhood of head injury if not done correctly (if not perfectly).
Most of my gaps are less than an 1/16th" to 1/8" from the vehicle interior.
I'll try to take some better pictures, I noticed there are none in my gallery.