Well i made the poor choice of buying the 80 amp alternator for the 5.7 npr, instead of the 70 amp for the 3.9. The 5.7 alt is a fair amount larger than the 3.9 alt so i had to make brackets. basically the 3.9 alt you can put a bolt through the standard mounts on the engine and shim it with nuts and washers to where it needs to be set. the 5.7 alternator has almost the same size mounts as the mounts to the engine so i had to make brackets to connect the two. As well, the pulley on the 5.7 alt is 1/8th larger in i.d. than the Luv alt so either buy a cheap aftermarket pulley to match the vbelt or bore out the stock luv pulley (as i did). otherwise works great, other than i need a lockwasher on the alternator pulley nut, it keeps loosening. charge is good, and now its 80 amp. I just need to wire the alternator to the relay so my engine light will shut off.
i paid 115 shipped i believe
http://www.amazon.com/Alternator-Isuzu- ... B003679BVI