Can't say I ever thought of using a moto shock on a mountain bike so have no idea if that is possible but my first thought are the vastly different needs required of each shock bike-wise.
Fox doesn't do custom length in mountain bike shocks, they do for mx?
"...the people get the government they deserve..." suum quique
yea, moto shocks deal with about two to three times the weight, assuming I think an average moto weighs around 350 or so? The damping and spring rates would be so far out the window it isn't even funny. It wouldn't work, plus good luck trying to get your wheels to mount, and it would most likely outwiegh any frame on the market by a fair margin. but try it and let us know how it works out for you.