That depends on how you choose to wire it up. The simplest way is to replace the rectifier directly and make use of the voltage control Ariel designed in; an option would be to use a modern regulator /rectifier and make better use of the alternator, maybe converting to 12V at the same time.
A replacement rectifier will have two DC poles marked + & -, and two AC poles marked ~. It doesn't matter which way the AC is connected. The old one will have one DC pole, probably -, with the + on the mounting stud.