I've got one of the original C6 flex plates if you want it, it's brand new. Bought it off U-haul a couple of years ago. This is the one that goes on when you have the cast iron flywheel. Pretty sure if I IIRC It has the 4" bolt ring and new bolts.
Updated: That backup ring is used so the bolts don't "tear" "mark" the flexplate, if the bolts "mark" the flexplate it will cause a fracture point. Hope I explained it right.