many years ago, Chinese glow engine manufactories copied OS glow engine as a criterion and retained till now, so all Chinese glow engine is same dimension as OS include the installations and muffler connection dimensions....etc.
40 series is a classical size all these years, manufactories always make three size on the same crankcase but different liner for different displacement. the three size is .40, .46, .52, later, nobody use .40 because almost same dimension and weight, but 40 is less HP, so they prefer .46 and .52, later manufactories want to make bigger on this size, they increased the <span sizset="2" sizcache08386887386580739="4940" class="def"><font color="#0066cc">cylinder</font> <font color="#0066cc">bore</font> to get the .56 displacement on the same crankcase of .52. so .56 appearred years ago.
GT9 is based on a .56 glow engine size, but the different output on Nitro and petrol on same displacement, caused on the dfferent fuel speciality. so usually 9cc is less output than .56 size glow.
NGH fuel-delivery-system solved the problem for fuel-transition just, it is with pump and regulator for petrol not for nitro, you can try other carb with this system is ok.others details  are all same. </span>