I use the back end of a caster SK10 (I'm sure that's similar to the D4) on my 2wd cobra racing hybrid. Front end is a hobao H2.
Going good so far only tried on mid grip astro. Only problem is that I need to run a reversible speedo as you can not flip the diff over. Not a problem if your just removing the front shafts.
This is the Facebook link.
http://www.facebook.com/groups/539051429511100/