Thanks to @TES737 for the design starting point and to @chrisqwerty for the Titan dummy design for reference: http://www.thingiverse.com/thing:1514324
This modified design of a Titan mount puts the center of the top of the hot end in exactly the same position as it does with the default extruder that comes with the 8" Pegasus.
I have an 8" Makerfarm Pegasus with lead screw upgrades and I'm not willing to give up print area. Designs that put the motor on the right run into the problem that the hot end is fairly far forward and so some Y print area is lost. Another issue is that the Titan is fairly compact and so the hot end is higher, and hence the Z axis is lower at the home position to the point that the X axis extrusions run into the couplers on the Z motors. Other Thingiverse designs have issues with the mount running into the ends of the X axis. This mount design should place the center of the top of the hot end in the same place as the extruder that comes with the 8" Makerfarm -- and so no print area is lost and the X axis doesn't run into the motor couplers. The motor needs to be on the left.