I'm not so sure that the Tower Trainer .60 would be underpowered with a Magnum XLS .46A on the nose. I think that would be a good combination with an 11x6 prop.
The Tower Trainer .40 Mk II is a terrific flying plane and a really solid value. A ball-bearing .36 or a Thunder Tiger GP-42 is the ideal engine for that airframe. The XLS .46A would be more than enough power, even if you decide to put it on floats.