I'm not familiar with the Cunningham floats. Are they foam core, or all wood, or fiberglass? If foam, I would recommend sheeting the bottoms at least, and glassing them as well. The bottoms invariably get beat up when beaching the plane and /or just sitting around.

The Evo .60 should be plenty for power, but a 4-stroke would work better for smoke. If you go that route, a .72 is perfect, plenty of power for floats.

Where do you plan to mount the smoke pump, and more importantly, the smoke tank? There's not a lot of room forward of the c/g on the plane. The pump is okay where you can find a place for it, you can add weight where needed to balance it. But if you have the tank significantly behind the c/g, you'll have a balance shift as the fluid burns off.

You'd either have to start tail heavy with a full tank, the balance would shift to neutral as the tank empties, or start off neutral with the tank full, which would change to nose heavy as the tank emptied. With the TME pump, about 2 oz. /min. is recommended for glow engines l.90 or less, so a 6 oz tank will get you about 3 minutes or better of smoke. If you can get the tank on the c/g, it won't matter either way. I have the H-9 Cub with floats, it's great on the water.