You will need the ADASCTLM27. This replaces the stock visual back and allows the use of AP 2.7" accessories. The reducer is an 27TVPH. You will also need the ADA2003. This screws into the reducer allowing the use of 2" accesories. (either EP's or camera nose pieces) All parts are listed on the Astro-physics web site in the price list tab.
NOTE:
You can also use just the ADASCTL27 and the ADA2003 without the reducer. This will act as the "eye opener" to reduce/eliminate vignetting with wide field AP's