Hey that's a great find!
The TC 90 was one of my first bikes back in OZ in the 70's. I have fond memories of racing around the farm with my mates on that bike. In fact, while my TC was smaller than my mates bikes (TC/TS 125s), it was certainly faster in a straight line drag
. Krikey, we took those bikes everywhere - rounding up cattle, through rivers, up into the bush in the hills, and 'racing' on motocross tracks. They were bullet proof.
However, I did have one big problem when the rotary disk valve disintegrated and got sucked into the engine. The countersunk screws retaining the rotary disk valve friction casing had vibrated loose until they rubbed on the valve and fractured it. When you strip yours down, check the condition of the disk valve, remove those casing screws and then loctite them back in place. Also, check to make sure the automatic oil pump is working properly before you get the engine running.
The high / low gear option proved to be useful in really snotty terrain and when rounding up cattle.
The bike you have found looks pretty original and would be worth keeping it that way if you can source the missing bits. Altogether, a super little bike which gave me a soft spot for Suzukis ever since. Good luck with the rebuild.