What I have learnt.
The ones with fewer cooler fins on the barrel are Chinese castings or the Chinese Powertorque and the ones made before are earlier Australian cast and have twice as many fins. Engineers must have figured that most heat dissipation occurs in the head and/or is most vital on the head, which is alloy. Less fins means less metal needed in the casting -saves $$ in production costs over time. Victa has always been looking for ways to shave costs and charge the same price for the end product. Why do you think they moved from the G3 to the G4/LM carb? Not because it was an improvement for the end user!
Another glaring difference is the long crankshaft version for the Tornado model.
Later versions had a starter with less surrounding metal, designed to carry a different plastic engine cover. That is what mainly differentiates newer models. A new cover design disguises it as a new engine when it's not, for marketing.
