Mike does indeed sell 8mm bore pinions, they would be an excellent choice due to their special hardening process, and Mike has excellent customer service.
There are several places to get the larger neus, mainly boat and plane online shops, though you can order them from Castlecreations (they are the USA distributor for Neu motors I believe):
http://www.castlecreations.com/produ...motors/nm.html
Looking around, there are few places with the neus in stock, especially the larger ones, as they are made to order usually, so the seller places an order with neu who then make the motor and ship it to the seller a few weeks later, then they ship it to you; quicker and cheaper to go directly to Castlecreations and order it up.
I wouldnt like to recommend an exact motor (kv or length), but the 2215 seem to be good for lighter 1/5 scale, and the 2230 for the heavier models, or models requiring higher top speed ( able to gear them higher as they produce more torque ).
Good luck with your project, I do like seeing the big 1/5 scale vehicles being built up- more of a challenge compared to normal 1/10 and 1/8 stuff