There is an apparent shortage of suitable rings for OTA's with 80mm diameters. Additionally, not many of us seem to actually like the Takahashi clamshell, so what are our options?
Here's the best option. Price is not small, but having used Borg rings before for my mini-guidescope (Tak 7x50 finder converted), I swaer BY them, not at them
http://www.sciencecenter.net/hutech/.../html/7083.htm
Additionally, Ted and Mia at Astro Hutech are great to deal with, and dispatch rapidly from California to here - last set I ordered was here in 3 days.
If those don't grab you, you COULD shim Vixen 90mm tube rings or the average-quality Skywatcher hinging rings with a 10mm aluminium ring, or you can apparently convert a set of camera telephoto lens rings. Also, there are 85mm tube rings available ex-China for MORE than the Borg ones, or Parallax, again, at a larger cost than the Borg.
I ordered a set for my newly acquired FC-76D (FS-60 conversion), and they will be sent today, CA time (there was a US public holiday yesterday)