As a very loose comparison a 20cc gasser is about the equivalent of a 1.20 four stroke engine in terms of power. Your 2 stroke 1.20 AX is about the equivalent of a 1.40-1.80 four stroker ( depending upon engine being compared ).

So a 20cc might be a good match to the 1.20AX is you bring the batteries, etc. forward to compensate for the light engine.