I'm a little confused by the rotating bottom part. Are you talking about having the shaft go through the bottom mount? Most motors come with a plus shaped mount that bolts onto the bottom of the motor. The shaft may stick out either end as long as you leave room for the shaft to stick through the mount. If you have the wires on the other end, you could mount the motor on the inside of the mount and have the shaft sticking through the firewall to the outside. Do you have any links to a motor like you're talking about?
The motor you are useing its ment to be either bolted behind the mounitng plate (inside the plane) with the shaft sticking out the other side, or useing an adaptor that screws into the rotating can with theose 4 holes you see there.