Yamaha produced various models of the TT600 over the years, with the more recent models being made by Belgarda in Italy for Yamaha. The TT600S had a more road orientated set up with electric start etc. The same roughly for the TT600E, The TT600R from 1998 on is a very different beast. Kick start only, plastic 10l fuel tank, alloy swing arm with fully adjustable Ohlins shock, Adjustable Paoli forks, Regina O-ring chain, Brembo brakes with braided hoses, alloy Termignoni silencer and so on.
I have a 2001 blue model which has done 20,000 miles of hard overlanding fully loaded, the only thing wrong with it is 5th gear (XT/TT achilles heel). I use a 20l Acerbis tank (have managed 300 miles on it) Rack, ally boxes, centre stand, crash bars etc all from www.offtheroad.de.
They can be a pain to start but so are a lot of big singles. Do not confuse with the "new" 2004 UK model TT600RE, this has electric start(no kick) but Yamaha have paid for it with non adjustable forks ,Cheapo shock (2" lower seat too) and a couple of other little cost cuts.
I have had the seat re done by bum wraps, my last jaunt was 8,500 miles trans Canada with 40kg of gear and my woman on board and as soon as 5th gear is fixed I am going Newfoundland-Alaska-Argentina on it!