Unleaded petrol does not act in exactly the same way as leaded, since when leaded burns the tetra-ethyl lead is converted to metallic lead, which lubricates the valve seats and guides on a 4 stroke. In the case of a port-controlled 2 stroke there are less likely to be problems but you would have to try it and see. On the other hand I'm not personally aware of Victa 2 strokes having problems on unleaded fuel.
One imperial gallon is 8 imperial pints, so the mix is 8x3, or 24 to one, petrol to oil. That means you would add 167 millilitres of oil to 4 litres of petrol.
