I think MK also does the billet alternator brackets? But there are some on ebay and others on google if you look for "cosworth billet alternator bracket)
Here is a link:
http://www.ebay.co.uk/itm/BILLET-ALL...-/121767548010
Anembo have them too:
http://anembo-engineering.mybigcommerce.com/
I think you will get over 680 to 700 bhp plus on that setup with the right mapping.
I think Mark Shead visited Norway recently to map a big power car, I have seen him map a cossie to over 700bhp on the same turbo as yours (MA Developments)