I reckon at some stage that bike has had a sidecar. Siamese exhaust, flat profile to the rear tyre, and I would expect to find the rear sprocket is the dinner plate 49 teeth version. Solo A10 is 42 teeth.
To proceed, even at a slow pace is a good decision. Remember these bikes were made at a time when the engineering was simple and the parts relatively robust. All the help is here, all that is is short supply is the motivation.
What can be done with your neglected machine is Roy's bike pictured above. Inside its all fine and dandy, outside it wears the years with pride, functions as it should, and I'd hazard it has been of more interest than one that has had ££££'s spent and only comes out on fine days. It really is the perfect cosmetics that eat up the cash and make you very wary of risking it out on the road. Not for me, I'm a cheapskate.
I could say half the work has been done already, the motor is out, in bits. For now I'd dig a little deeper into the engine failure. Some more detailed pictures of the damage. Meantime take steps to prevent more deterioration. Get that WD sprayed on, give it a rub and make a start. Just giving it a good clean and a rub over will transform it, and is good enough for now. Keep a logbook of what you find, what you did, what it cost. Some would remark to keep this in a very safe place.
I said safety critical parts have to be A1. Brakes, Wheels, Frame. I won't say wheels are critical during a restoration, as long as they turn you have a rolling chassis. But they can be left 'til last and there's a good chance that over time a better pair will come along. Even as they are, the hubs are the part they no longer make so should be kept. These days they can do powder coat that looks like chrome, this looks OK even on sound but pitted surfaces. Chrome shows every blemish, so Rex's suggestion is another excellent and cheaper option when the time comes. Same for that scarred barrel, it can be repaired, cost being the only barrier, so hang on to that for now, it will be worth something to someone, sometime. I would never scrap original factory parts if I could help it.
Swarfy.