I have taken the 1.75mm version of the original extruder and removed a cut-out to fit the top of the J-Head Mk V-BV when mounted with a Version 5 of the mounting plate. Some slight support was also added to increase rigidity of the part above the cutout.
I have tested this design and it works well.
I have no immediate plans to make a 3mm version unless someone requests it. I do not use 3mm filament so I have no way to test it.
I have added the beefed up idler arm I have been using with this extruder since it appears the original design by Tito has been removed from Thingiverse. My idler is slightly less prone to flexing anyway.
You can fit two of these onto my x carriage design for dual extrusion: http://www.thingiverse.com/thing:156389