[suicideneil]

4.6" is tiny, I'd think about something atleast 5.5" really- stick a piece of drainpipe over a normal MT rim, then stretch a rubber tube over that...

As for the motors, you cant hook an inner to a diff, they just dont develop enough power or torque to turn such a high gear ratio (only reduction is the diff)- even with one motor for each axle. Big outrunners like Turnigy or Holmes hobbies sell would be the ideal thing, but like I said, its a tricky thing to choose the perfect one as you can adjust the gearing, only by using smaller or larger wheels & using buggy or truggy diffs.

All said and done, there are MT foams available from a few places (Imexrc.com), or the HPI Phaltlines work well if you tape the insides and glue them to the rim well.

Using larger pinions has the same effect as using larger wheels after all, so it would be easier to find the right sized wheels that wont fly apart, rather than custom ordering massive pinions.

That, or find higher kv motors to use- the castleneu 2650s would still work fine if you have two of them in one truck....