We used an Edge Racing alternator, saved some pounds, worth the effort. We just made two brackets to mount it to existing bosses on the engine and then used a string to figure out the belt length. I recall that Cosworth was offering a kit for 2.3 Duratec that included mounting bracket and belt but it was for 2.3 as configured in Formula Atlantic use...and if memory serves it didn't fit our 2.5 (though the details of precisely why escape me at this point). So, I got just the alternator somewhere online (that also escapes me at this point) and took it from there.
Did a Google search just now and found some info on the units in UK HERE
It does a great job of charging the battery but ECU does not like it, gives me a 'battery' light. I imagine Mike at MotoEast could turn that light off forever but it does not bother me enough to do anything about it.