Many thanks for the helpful answers.
To answer Nick, the only part of the vehicle would be the battery box at the front and I need most of that for a or some batteries. It will be worth seeing how much space is left though.
I have determined that the original bell would be the sort used as a fire bell in or on buildings or a school bell.
A remote door bell would not be suitable as it needs to work from a push button on the end of the steering tiller.
Brian