I'm currently in the process of putting 400ex spindles and hubs with yfz450 calipers on mine.  The dual piston yfz450 calipers bolt right onto the 400ex spindles.  To get the 400ex spindles to work I had to get a set of lower balljoints that are for aftermarket 400ex arms.  This should be quite the upgrade.  Way way better braking and much better wheel selection.  I need to get that thing done, the weather is finally starting to get better.