I have one on my 5.0. It will fit both 2G and 3G alts 5.0 or 2.3L
I got mine from ASP. It's 1 7/8" in diameter. I put it on with my underdrive pulleys and it compensated for the slower belt speed. I didn';t notice any difference in charge at idle.
Well it's definatly made a noticable improvement, i can run the defroster, air on high, windshield wipers, Lights, and cd player all while idle and my gaugh stays about the middle, unlike before