Alternators are UGLY 
Prob of alternator is, that they are made for top-speed
of 16000 to 22000 rpm (today). Ratio is created to meet
top-revs of engine with top-revs of alt.
Not having the space to get this ratio into your A, you will allways
have a real high "start-rev" of the alternator and not reaching
the built-in-power .... 
You will run the alt powerwise way below "design-speed"
(no prob if output is sufficient to your needs)
Low revs of alt is a good thing as bearings will last forever
