On this side of the pond, we usually install a low cut in regulator into the alternator to facilitate the use of the OEM pulleys on lower rpm engines.
Many fellows doing a generator to alternator swap on old tractors and machinery opt for this as these machines spend more time idling than they do high rpm driving.
The GM 10SI alternator uses a one wire hookup to make things really easy.
I also found a guy in the USA who will build you an entire alternator inside the original generator field casing; outward appearance is that of a total stock generator with new alternator technology inside. Check out
www.gener-nator.com