Not super smart, but by the good fortune of good timing I can maybe get you pointed in the right direction. The bracket is fabricated using instructions supplied in a back issue of EAA Experimenter - from 2004 if I recall. The starter itself is an automotive starter. Depending on the number of teeth on your ring gear it may be one of several variants.
Best thing to do is do a search on the EAA site for the article.
BTW a local builder happens to be fabricating this exact setup right now. The main attraction for him was low cost - CAD$65 for the starter from an aftermarket auto parts supplier. I would ask him for more details, but he just happens to be in a funny little place in Wisconsin right now...