I have uppdated my Geeetech Prusa i3 with E3D Titan extruder and hotend.
And at the same time I also uppdated to lates firmware version of Marlin.
If you want you are free to download my Configuration.h at your own risk.
With this youtube clip and text a want to share how I did and hopefully give you some idea how to do.
Parts you need to this project
1.E3D Titan extruder (extruder, motor and motorbracket
2. E3D hotend
3. Some aluminium plate
5. Welding tools
6. firmware from http://marlinfw.org
I need to make some aluminium plate to hold the extruder as you can se in the youtube movie.
After i have mountet extruder and hotend I also need to Uppdate my firmware.
The only part you must uppdate is DEFAULT_AXIS_STEP_PER_UNIT to 837 if you buy 0,9deg/step motor.
But I aslo update to latest version of Marlin.
I also need to take some connection from old extruder and hotend and weld to my new cable.
The only problem I have was I need to adjust my stepboard to 1,1v.