RE: 4-stroke to 2-stroke....
As if I need to muddy the waters any more......
I have a World Models Zen 50, which is roughly the same size and weight as the groovy 50. World Models calls for a .52 sized 4 stroke on it, and truth be known, it would fly the plane, and probablly be enough power to make it fly most of the pattern manuvers. I fly mine with a Saito .82, which is very much overkill for the airplane, but it's still not screaming fast.
So. My input is as follows. Not really knowing what you're expecting out of the airplane, I'm guessing here. I don't think a .46 LA will do what you want. Sure, it will fly the plane, but you're going to be very limited in your vertical manuvers, and I really think you'd be working to get the plane to do a lot of the pattern manuvers. A .46 AX would be better, but it think you'll still feel the need for more power. If you want to stay 2 stroke, I'd suggest a good .51 or .61 sized engine. 4 stroke, I wouldn't go below a .72.
Just my two cents....
Andy