It's obviously an old boat and may well have been through a dozen owners who may well have messed with it,in various ways.
It was probably originally direct or indirect raw water cooled and had a Jabsco type water pump fitted,and to line everything up may have involved putting spacers in the pulleys. It is possible to only have one crank pulley operating both the alternator and the external water pump,but the engine pump would need removing and a blanking plate over the orifice for direct raw water cooling.Indirect raw water cooling would need a double crank pulley,one for the external water pump,and the other for the alternator and engine water pump. Never had my crankshaft pulley off,and looking at the online manual,there doesn't appear to be a spacer,so I would assume that if the correct pulley is fitted then everything should line up.
Don't understand why there are two skin tanks,unless one was too small or has no baffles and the engine was overheating. (supposed to have one square foot of cooling area,per four HP) for the BMC 1500 this should be about 8 square feet.
Boater Sam has covered the sluggish starting.
I have owned my boat for two years now,and have just about fixed all the previous owners' bodges!
If I did need to remove the crankshaft pulley,I would have to ask this excellent forum; 1,How do I lock the engine up in order to remove the nut,and 2,Is the nut RH or LH thread?