Cr&p design alternator on the 3.9. I bu66ered mine up at the weekened playing in a mud run at Slab Common. I had a spare alternator so not a major issue. A bit awkward to get to the lower bolts but do'able. The problem is that to get the belt on you have to take the alternator off, I only found this out after I had refitted the new alternator The adjustment with the sliding top bolt is insufficent to get a new belt on, so you have to take out all three bolts. Very awkward, even at home in daylight with all the right tools. Must be a nightmare to replace at night on the road.
While I was doing it I changed all three belts. To my suprise, the inner belt (PAS) was split with about 1mm remaining and the fan belt was not much better. Getting the new inner belt on is also a pain in the arse as the PAS pump only slides untill it touches the block and it could do with more slack to get the belt on. I had to turn the pump while levering the new belt on the pully with a thin blade screw driver, a three handed job:)
I thought the whole job would take about 30 minutes in the end it took me about two hours to replace the three belts.
My guess is that most inner belts (PAS) don't get checked or changed that often, so best check yours now before it fails.