Archemedes Penta 3 cylinder 2 stroke

[popswoo]

Can anyone tell me how to replace wter impeller on this engine.There are 6 bolts holding gearbox on and an oval apature to disconnect gear lever.ihave undone the 6 gearbox screws and the gear rod is disconnected but I can only move gearbox about 10 mm.
Regards
Dave

 

[alb40]

I dont know this engine in particular, but most outboards just need a little smack with a hammer to help seperate them.