Sorry about the late reply, it took some research to find an alternator to fit the bill. You're current alternator appears to be a Bosch unit, and those don't go much higher than about 115 amps, and the cost for us to upgrade one would be a bit too high. As we would have to have one imported from England, and to upgrade it you would need an external rectifier.
But I do believe a Ford 6G series large case alternator will directly fit, and we can pump those up to over 200 amps, but the post between the States and England is a bit dodgy, so it would take some time.
This page should have what you need.
http://store.alternatorparts.com/1999-2008ford73l60land65lpowerstrokediesel.aspxThis is the exact alternator I recommend, but it may need the mounting holes drilled out a bit.
http://store.alternatorparts.com/partnof1-8253m-hd200.aspx