I don't know what you should do. When draining the oil, is the motorcycle on the center stand or otherwise level?
Without running the engine, I might consider flushing the engine with kerosene or diesel fuel & do a final flush with cheap engine oil to remove as much of the kerosene/diesel as possible. But someone else probably has a much better idea.
I don't think the KZ305 has an oil pan. On a KZ650 I would remove the oil pan to see how bad it is.
On your bike, I guess you could remove the clutch cover to get a look inside, but I don't know how helpful this would be.
EB photos might be of use if you're unfamiliar with the 305 engine.
1981 KZ650-CSR. Competition, Sports & Road.