Ryan,
To do the XXX CR rear end you ONLY need the wishbones and hubs. The toe in blocks you'll already have 1 set on the car. What I would say though is these do break (I've broken these but never, ever brokena a rear wishbone) so getting some spares would be a wise move. Personally I use 0 deg and washer accordingly, but each to their own.
You should not need any mods to driveshafts, the driveshafts on all Losi's are the same with the exception of the BK2, which have ever fitted an x5/xx4 with any mods. Edit, just realised the possible point of confusion, the cvd's and dogbones are fundamentally the same dimensions, it's purely personal choice as what to run. For me I always run CVD's!
Gayo, I think it's in part becasue the link is a little longer and higher at the outer end, where as on the old CR hubs , the height was not adjustable and got lower towards the outer hole. Of course as with so many things, it might all be in our heads
I've yet to try Short VLA.