I'm not familiar with the vehicle, but after looking it over on the Tamiya website I think you'd be better off with a Castle or Tekin 1/8 brushless combo on 4-6S lipo. Tamiya lists it as a 1/8 truck and it looks to be similar size to T-Maxx, Revo, Savage, etc. I don't think the VXL system would work out, at best it would get hot and be underpowered, at worst it would go up in smoke.
I haven't seen one of these converted before. There are a few different things that could work, depends how much you want to put into it. You could make a custom mount, and keep the transmission (although not sure the 2-speed would hold up or be the best choice). Or you could get rid of the transmission and go for a center diff with the RCM mount:
http://www.rc-monster.com/proddetail.php?prod=rcmcdmm You could also use one of the other mounts from a variety of buggies and truggies and use the center diff assembly from one of those.
I don't know if the RCM Revo mount could work, might look into that too.