Not single-engine.
Except the single-engine requirement.
Except it's multi-engine.

The Lycoming GO-480 series was typically just 270 hp. Some, like the GO-480-G series went up to 295 hp. These engines are common upgrades on Republic RC-3 Seabees.OEM is a B9F Franklin = 215. many have the 350, GO480. upgrade.
Grumman Goose. Gets the following with no mods:
ME
Tailwheel
Complex
HP
Seaplane
I was thinking Widgeon, but you'd have to find one with more than 200HP per engine.
Meyers, Spartan Exec, BE 18, Cessna T 50, Goose, Widgeon, Duck Seabee, Twin Seabee.