I bought a PowerLite unit from Eurolec Components:
http://www.eurolec-components.co.uk/cms/index.php/products/starter-motors/ I recall there was a bit of an issue with the mounting adapter, as the starter motor need to be turned through about 30 degrees or so (if I remember correctly, as it was about 7 years ago) to get it to fit. But they were happy to supply an adapter, which is an aluminium circular billet with a series of holes drilled through it. The starter could then be rotated about its long axis until it fitted correctly.
I hope this helps.
