Peter.
I take it from the sounds of this that you have a dynamo on it at the mo?
It isn't THAT simple although can be done without too much trouble.
For what you will gain, my own opinion is to stick with what you have. I have ran a few classics with dynos and haven't really had a problem - as long as you bear in mind not to overload the electics in slow moving traffic.
Thats the only main benefit. With an alternator you can run the heater, heated rear, radio, wipers, lights etc while the engine is at idle without flattening the battery.
Depends what you want out of it and whether it is worth the trouble!
Johnny.