Well looking over the Wiki for the Hephestos almost all of the printer looks like a fairly well designed i3 with the exception of the witbox extruder and it's special mounting bracket. You should be able to swap in a Wade's with any other hot end with minimal difficulties. I did find a place selling just the
hotend but it sounds like you want the complete kit.
Of the hotends that seem popular right now I would go with
Prometheus hot end for a high end system (and it seems fitting to have Prometheus and Hephestos working together.). Or a actual
J-head if you are going a bit cheaper.
Thanks Mike