i may have missed it, but you didn't say how high the projector will be mounted. how high is the top of the screen?
the easiest thing i can suggest is to take a laser and hold it at the spot where the projector's lens will be. if you can hit the top right corner of the screen, you should be fine. all you need is line of sight from the lens to the screen
Displays: Samsung PN64F8500/JVC X35
AVR: Pioneer VSX-1130K, 7.1/5.1.2 audio
Sources: HTPC(Enby), PS3, XBOX360, Wii
Control: Harmony One