Hi I plan on using a similar reveres setup to Tilly819, you may find his posts and pictures if you do a search.
He is using a seat ibiza starter motor and a ring gear from MK engineering, it works a treat apparently. He said MK are reluctant to sell you the ring gear separately though, this gear sandwiches between the diff flange and propshaft with the starter underneath.
I've heard the reversing boxes can whine and also cause vibration, plus they arent for those of us on a budget.
Hope this helps also Chris.
I found the thread.
http://www.haynes.co.uk/forums/showt...hlight=reverse