The number associated with that "chassis" is over 90 million since inception.
If you are restoring it to factory original, you will spend some serious scratch.
I have a 68 CT90K0 that is a Junior First Place bike. My friend asked me why I didn't have it judged when my RE5 was done. I said that it was my pit bike, why would I have it judged?
The rest is history. All real, all the patina, first place. Cannot tell you how much money went into it, but it look like it was dragged out of a barn yesterday.
I also have a 79 CT90. Totally original condition. Very low miles.
There are a few parts laying around here for CT90s. Nothing 1973 specific. Let me know if you need something.