Just finished building my TRF416.
I had to add four extra 4mm shims to the center shaft to remove the slop. I don't see the need for bearing holders on the center shaft unless you need that flippable one to use larger spur gears.
I use the short reversible suspension arms, so I didn't notice the slop in the normal arms that came in the kit. I use 1C(old)/1B suspension mounts at the front and 1A/1D suspension mounts at the rear, and I used the spacers as in the manual with no binding - I just lightly tapped the suspension arms with the handle of my hex wrench until the suspension arms moved freely. See the "TECH TIP: Suspension Unbinding" post in the Xray forum at http://forum.teamxray.com/viewtopic.php?t=2872
to see what I mean.
The steering setup is a tight squeeze, but I don't have anything touching anything else. It is great that the steering mechanism has no slop, unlike my TRF415MS which I had to shim like crazy to remove most of the slop.
By removing the O-ring from the one-way cups you can use the steel 46mm swing shafts from the TRF415, at least until some steel 44mm ones become available. The new swing shafts are slightly thicker than the old ones, though.
I really like the new C-hubs, they aren't as wide as the TRF415 C-hubs and as such the steering is not limited by them. The old C-hubs fit, though, which is a bonus. The new wheel axles do fit into the TRF415 wheel hubs with the old bearings, which is also a bonus.
I think the rear diff can be improved slightly - I like that it can be externally adjusted and comes with an aluminum diff nut (finally!), but I don't like how the diff balls can be seen and hence are open to dirt - the TRF415MSX MRE-onwards "sealed" diff was much better. Also, the inner hole of the diff plates should be molded to the diff joints instead of being circular, like in the TRF415.
I have noticed that the belt stabilizer doesn't actually touch the belt, is that normal? I assume it will touch the belt when the car is moving?
The car went together really well and I am extremely happy with it - already sold my trusty TRF415MS. Things to look forward to - steel 44mm swing shafts, aluminum rear hubs, molded diff plates, improved/"sealed" diff pulley, and the Novak GTB/13.5 brushless system sitting under my Christmas Tree!