Originally Posted by
EuropeanAM
In theory, removing the 5" extension is not that difficult. Some hardware must be changed, etc.
However: The gearcase is a bit of a different story. Not quite as simple as "just pull the 25" shaft out and shove the 20" shaft in": The entire gearcase must be reshimmed.
Additionally, it is very important that Mercury be on board with these changes. Otherwise- there may be problems in the future as the serial number and model number will not match the engine's configuration.
You might be wise to make a phone call yourself just to explain the situation and find out how to best address it.