Hi Stuie. Apart from the rigid frame another thing of note is the so called Longstroke engine, the gran'daddy of them all. Rare these days, but perhaps a bigger bundle of trouble ahead. It seems unusual to have a well presented frame, tank etc, but a motor that looks untouched.
Biggest problem is Camshaft wear, the later design runs the cam in an oil trough, absent here. Good news is that Hepolite/Wassell market new Cams made from precious metal, judging from the price. I'd be inclined to strip off the timing cover, remove the oil pump and free it off, rather than just jumping on the kicker. Your engine is the earlier version, two bolts (not 3) at the base of the timing cover.
By reputation when well set up they are a nice ride, more for sedate cruising than thrashing. Rear sprocket should be no more than 46 teeth, any larger suggests an ex sidecar bike. Service Sheet 210 shows how the rear brake lever is set up on a Rigid Frame..
Welcome to the Forum, it will be interesting to follow what you find.
Swarfy.
