A lot of KC16 carbs that came on the 25SS race motors were re-stamped KC15 carbs.  Since the carb bodies are the same Mercury just changed some parts around to come up with a racing carb for the 25SS.

This is a 15A carb converted to 16A specs.  It has a full butterfly and a throttle cable bracket.  Carb is clean inside but has not been run for years so, it may or may not need a service kit.  It is 1 1/16 bore and also works well on 20H motors to replace the KA7A carbs which have a 1" bore.  This is a fixed jet system, no leaky hi-speed needle valves to deal with.