I've never once had the need for two extruders on my Creator Pro, but as I am keen to use some exotic filaments and to get more consistent prints I decided moving to an E3D V6 Hot End would be a step forward.
If you haven't discovered E3D Hot Ends yet, you should check them out, they make some brilliant products including a 2 input / 1 output hot end and a water-cooled quad hot end: http://e3d-online.com
I initially made a mount that fitted on the existing carriage, however it wasn't perfect as the existing carriage was obviously not designed with the E3D Hot End in mind.
So I designed this carriage.
The bearing housings work exactly the same as the original Creator Pro carriage, just snap the bearings into place. The belt anchor from the original carriage can be used with this carriage.
Just fit the Hot End into the mount, place over the other half of the mount and secure with suitably sized M3 screws through to the extruder stepper motor. The left extruder motor should lineup perfectly with the top of the Hot End.
I have fed the heater and thermocouple wires through the space under the stepper motor.
You may also notice I have an extra piece of plastic in the images which the wires are cable tied to. This was just a 20mm x 20mm x 10mm cube that I had lying about which is primarily there to allow the end stop to press the carriage. I plan on incorporating this into the carriage on a later revision. I will also be changing the other side of the carriage to allow for a cooling fan next to the nozzle.
I printed this in PLA, with the right hand side of the carriage on the print bed. It gave me good results printing with my Makerbot Replicator 2.
I plan on printing this in Either PETG, ABS or Nylon in the future on the Flashforge Creator Pro.