I rode enduros on a TT600 back in the mid 80's and despite its weight, loved the living shit out of it, its right up there as one of the best bike's I ever owned which is saying something as it replaced my 490 Maico GS. I didn't do a lot to it other than have someone or other revalve the shock to suit more serious work, and upgrade the forks with YZ490 dampeners (or was it IT490?). I modified the pipe and fitted a White Bros muffler. In the 4 years I had the bike it never had any major dramas, the only biggie being the nut that holds the counter balancer had come loose and I'd have lost the counter balancer and probably the engine. Luckily I caught it in time, which is weird as it's something I'd never previously checked...Karma. I also fitted an Acerbis front 'guard and headlight, only because the originals were rooted. I'd like to use a TT600 motor in a dirt tracker, I know the earlier TT500 motor is more popular but the 600 despite being a big lump of aluminium is still a good thing. I can recall Head (Neil) on this forum having one with USD forks and a lot of other tricks and Yamaico Pete might know something about our Californian mate Marsh Runyons TT which was bored and stroked to something like 800cc. Pete may have raced it while in the US, I know Edgar Phipps raced it and raved about what a torque monster it was.