I have been using E3D hot ends (dual) for a while. E3D hot ends are top notch, but they use fans, which sometimes cause warping or delamination especially when printing ABS. Converting to liquid cooling addresses the problem and also makes the hot end a bit shorter.
The 2.5 mm wide cut feature in the top part can be removed if your extruder design allows it. My release of the i3ext works fine with the cut feature removed.
The design is only for the top part of E3D hot end. Heat break, heat block and nozzle are original, buy them from e3d-online.com website.
Then buy a water cooling sleeve from eBay for example. It is intended for R/C use, and for 20 mm motors.
Assemble using the instructions from E3D website.