The LT-40 would carry floats if it only had an OS.40LA. I have buddies that fly Kadet Seniors with no more power than that.
A nice ball-bearing 45 or a .70 4S will give you more power than you need. You'll see the extra power in your steep climb angle and shortened takeoff distance.

The beauty of Kadets is how slowly they can go, not how fast. If you put in a 23CC gas motor the plane would only be too heavy but probably no faster.
Then again, too much power is not enough for some guys.