Many of the TT600 and the XT660 parts are interchangeable in terms of mountings, same oil filter, brakes and some engine parts so it's probably not as difficult as you would think.

The tank is so small though, at 10 litres (inc reserve) it's not going to go far between fill ups. and as you say, there is nowhere to stuff the FI bits, certainly no room under the tank! Could try matching up the 660 motor to the carbs off the 600 ?? dunno if it would work though, need some specialist help I would think.

The TT has a dry sump so you could re-use that, but the rad is going to be a problem, maybe look at a side mounted rad and an air scoop ??

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