Darren, Mac's are good at range and pricing, but the proper water pump kit for the double pulley truck pumps (79-8591) seems to be perpetually out of stock with them, and you might need to go on a back order waiting list.
If you need it quick, or want to step up in quality, try
Mike Davidson in South Australia for his aluminium pumps. Keith Webb has just fitted a pair of these to the Swiss F15, and says with a coat of paint, you'd never know the difference, but the quality and reliability are much better than rebuilt originals.