Tiger cub first start in 48 years

I have just had a 1955 cub going for the first time since 1978. I changed all the oils and cleaned the oil tank out a couple of months ago. All the oil had drained from the tank but wasn’t in the crankcase. The engine is smoking badly from the exhaust. I just run the engine for about a minute. I couldn’t see any oil returning to the tank. The engine actually sounds quite good, with no rattles.
It’s not my bike so I have no history.
Any ideas please.

Oil doesn’t evaporate mate, so if the tank was empty it’s because of one or a combination of the following:
It was all in the engine (some could have gone into the primary).
It leaked out.
It wasn’t put in.

Smoking out of the exhaust could many things:
The sump WAS actually full and oil is being forced up the pushrod tube.
The exhaust / silencer is full of old oil and shite.
The valves / guides are shagged.
The piston rings are stuck in the ring lands and not sealing in the bore.

Oil not returning could be something like a shagged oil pump, but more likely just that you didn’t run it long enough.

Used engines don’t like being stood for 48 years. And you have no idea of the condition it was in when it was first parked up. The list of possible things to consider is rather long …