Oh yeah, Tamtechs are bombproof.
Mine is an original GB01 with GT01 chassis and front suspension. The chassis adds 1 1/4" wheelbase. I only needed 2 parts bags from Tamiya, $18 shipped, but had some other metal hardware leftovers from other tamiya models. I did a little write-up on the swap here.
http://www.hyperminis.com/gt01-chass...uggy-t376.html
As to the 12mm hex wheels bolting up to the GB02 frontend. I had a thought. The GB02 front is just a round piece 10mm right, so stock tamtech 10mm hex wheels bolt up? So you maybe could do one of two things. You could take a 12mm hex and drill the center out to 10mm, to slide over the GB02 hub, or make a simple round sleeve/bushing out of 12mm rod with the middle drilled to 10mm. Pretty much anything to keep the wheel centered would work I think. Of course this is all without ever holding a GB02 in my hands. The GB02 suspension always interested me, some day I'll build a mini Sand scorcher out of a GB02.