Happy new year Darren, mate they hoot when set up right, my cousins used to race one in a DT Sidecar and they were a weapon on US Flattrack back in the day.
If you buy a 69 model it'll even be eligible for pre70 class. I'm working on a very similar project only a 250.
I'm only gunna lengthen the swingarm, brace the frame in a few spots, fit a better front end, fit alloy guards and smallish pommy style seat.
Go for it, my brother has a shipload of bits for them if needed.
Cheers, Steve