Gold shocks look like they're from an RC10, as are the white shock collars that are now on the right hand car. Kyosho Optima "option house" shocks didn't have the hex at the top of the shock barrel.
My XLS had one-ways - was this one of those cases where later kits had upgraded components?
Both my XLS and my Procat had the same top deck as the left car. I've seen that one on the right but I don't recognise it. Maybe a later release?
Car on the right definitely still has the old integrator diff at the top, and the left car has the MMS layshaft as Moozo said.
The alu block to which the rear shock mount is attached is not the standard bar or z-bracket - perhaps to facilitate the rear-mounted shocks? Difficult to see from the picture but if those are standard wishbones in reverse then there would be some degree of toe-out at the back, unless the lower pivot blocks were also changed. The shock bracket is also non-standard.
You can see the Procat rear shock bracket and wing mount in the foreground of the picture - this was different to the XLS so at some point, some Procat parts were purchased if neither of these two started life as Procats. The chassis are both XLS standard stick pack (though obviously it's relatively easy to 'upgrade' to the stick chassis and the chrome wheels are from the XLS too. I don't see any Procat wheels in the picture.
