[OXO cube]

not syre if this will help but :-

not an s-can , but Team Slot do a 4wd motor 

Ref: TM-51004

Team Slot Motor TS5 4xPower.

and Avant do a long can 4wd motor 

Ref: AS20107

Avant Slot Long Can Motor Hunter 4WD 25.000 rpm

I'm pretty sure Scaleauto did a 'sprinter 2' long can as a direct replacement for the SCX 4wd motor 

also i recall reading somewhere that the front wheels should be geared to turn a little faster than the rears ( or is it the other way round ) 
but i have been known to be very wrong , very often hehehehe

good luck and have fun with your project , don't forget to keep us posted with your progress bud 

Kev