yes mongoose is S class gearing as is The TM Evo version
S Class gears VS origional G4
Second spur gears are slightly smaller than the original G4, the second pinions are the same diameter.
First spur gears are the same as the original G4 and the first pinions are a different size (slightly bigger)
So if you go to S class second spur gears you should go to S class first gear pinions