To answer the second part of your question, a .61 size engine on an LT-40 is too big. There is an old saying, "You can't make a racehorse out of a mule". The LT-40 is a basic beginner's trainer and isn't meant to do anything other than basic in flight maneuvers. However, it is your airplane and your motor and you can do anything you want with it. I personally would save up and buy an airplane better suited to the .61 engine. A SIG 4 star comes to mind.

Regards,
doubledee