I was also concerned about the 2.75" vs. 2.67" back focus and which one I should use. I called Tele Vue and talked with David and asked him which number I should use for a KAF-16200 sensor with 34.6mm diagonal, and he told me to go with the 2.75" value. I hope this is correct, as I already placed my order with Precise Parts for the 2.4" to ATIK EFW3 M54 adapter. If he gave me the wrong number, then I will be about 1mm to long even if leave out the 1mm shim. I will not be a happy camper if they gave me the wrong number.
Good info about guiding from the rings. If I have to go the OAG route then I will have to start all over again with the spacers and likely have to go back to PP again for another adapter. I just receive a new 1600 mount with encoders. I haven't set it up yet as I am still waiting on a few parts. I have been following the unguided discussions on the board with interest. Maybe I will get lucky and be able to image without guiding.
Thanks for the heads up about the spacing above the saddle. The good news is I think I have a solution already for this issue. I had the same problem with a Lunt 80mm solar scope. If I mounted the scope directly to the saddle the dew shield would hit the saddle and it would interfered with the etalons. To solve this problem I got a Male to Male D Series Adapter (DMM12) and two D Series Female to V Series Female adapters (DPA-VPA-FF) from ADM. This got the scope up off the saddle by about 1.5 inches. It also gave more flexibility when it came to balancing the scope as the Lunt is very back end heavy. Assuming I can get a Vixen style dovetail to fit the Tele Vue Rings, I should be OK. ADM has a VDUP7-V Series dovetail that should work, but I am waiting to get the rings so I can check the measurements with ADM.
Thanks for all the helpful info. Glad to hear you are happy with the scope.