I built a SIG LT-40 and fitted a 61 size engine. I put the radio in the back , and the c&g is perfect. When I was living in England , and building planes, I always found out that fitting bigger engine than normal makes the plane take off much better when on grass, plus plenty of power to spare if you get into trouble. My 52 inch span plane did have trouble taking off on grass (the recommended size was a 30, so I put in an 45 and wow it flew much better, so in a nutshell the Lt-40 will fly even better with a 61 than a 46 (just change the engine mount, it's easy)