How many projects do you have going?! This one will be awesome I'm sure.
The motors you linked to have been real hit or miss, some burn up immediately, some last. IMO I would choose a higher quality motor.
These:
http://www.rc-monster.com/proddetail...d=RCMdiffshaft will get your hyper 7 cd outputs down to 6mm. With that could you use traxxas center shafts? (the original t-maxx tranny had a 5mm output shaft for the 5mm side of the equation)
Just a thought. Regardless, I'll be watching this build!