All boats handle best if slightly trimmed by the stern in still water and not moving. This is because when underweigh a boat will trim by the head and as such will not manoeuver at its best.

Design considerations in the model with regards to the prop shaft will also dictate where you can put the motor.
If at all possible it is probably best to have the motor aft of the tipping centre of the boat ad unless it is a twin screw boat on the centre line.
As you have rightly said your batteries are the major weight and their position will dictate where you put your motor and any ballast required.

Tend to agree with Harry B on this. The other major point to consider is why did it happen and has any additional damage been caused. If there is damage to the head then you are looking at serious money, even up to it being a Total Constructive Loss, (TCL)
It is difficult to blow a head gasket on an outboard.