check out the chief mfg wma-300.
it puts the center of the projector about 18" from the mounting surface.
however, i'd check on rear and side clearance requirements of the 8700 before
i used this mount. a 1.5" NPT pipe of the proper length (custom cut at a local
HD or equivalent) may be necessary to get the projector to the proper height
relative to the screen.
(we used the wma300 w/ the rpa-021 for my dad's hx-1 project.
it was usable since the wma-300 was mounting in front of the opening to the kitchen
so no rear clearance issues were involved)