I mixed the latest (V3) version of Airtripper bowden extruder (http://www.thingiverse.com/thing:35404) with Terenceangs geared airtripper extruder (http://www.thingiverse.com/thing:456095). The latter was an old version of the extruder body but I used the gears from it. I removed the parts that weren't necessary for the new motor position and added a M10 nut for the bowden couplers (the ones that e.g. E3D ships). The main axle is a M5 screw for the MK7/8 driver gears. The whole for the bearings are 10mm. I found these smaller ones in my local hobby shop. Use the instructions from the Airtripper. I use 3 m5 spacers between the big cogwheel and the case, to keep the angle straight