Single blocks at the back are going to be a tight squeeze against the motor mount and at the front you're going to need the ones that clear the belt or get very innovative with a dremel and/or spacers.

Not overly enthused by the level of improvement (let's call it that) over the 418. It seems one might as well just buy a chassis plate and swap over all the hardware (if it is deemed the plate is in any way a liability).

As for the motor mount, I like the Yokomo style better. I don't see why Tamiya doesn't want to cantilever it (apart from maybe saving a few pennies on hardware manufacturing).

The diffs might be improved, but then again, there's some really nice diffs on the market from others and guess what, they fit in with minimum of effort (if not directly).