Wheel-base (axle-axle) is about the same as a ZZ. From rim to rim, they're about 2 Bits wide. I've never owned a Shen, so I can't say if they are or not. PCB is labeled: JYA09 03/05/15
I think the Bit swappable parts on here are:
-Batteries,
-PCB,
-charging setup (with minor modification)
If you're into modding stuff, these open up more possibilites:
-Hardwired motors
-Gearboxes
-Rims (think dubs, but like 4 feet high)
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These could probably stand removing the light, a bigger main capacitor, better tires, repainting/modding the goofy body, and if you wanted something more like a Bit a whole new steering set-up.
But as a "stunt car" it's very well suited for that. Giant rims, but can't climb. Fast setup, but it can't drive in a straight line...
And just for the record, the gearboxes are close enough tolerance that you shouldn't bother talc-ing them.

Oops.