I would go with a little larger engine thatn the LA40.. I have flown the Kadet Mark II for years and two different engines, even tried electric on it once. In fact, the wing on my Kadet was from the original Sig Kadet in the 80's before there was the "Mark II."

I currently have a K&B 40 in mine and it flys well, but marginal on the "umph" factor. I would not try this setup with floats, which I wanted to do at one time.

So, if you are looking, I would recommend going for a nice OS 45 if you want an engine to take you into the future. Or, even something like the Tower engines should work fine (I have not tried that brand, but some people really like them). If this is not your first plane, it would go very well with a 4-stroke and sound like nostalgia in the air