You can use a Duralast/Alternator DL7157 on the DS only because it does not need to have a isolated ground or a Wilson Electrical, Part Number: WIL 90014277 that does have a ground, but is expensive. PS must have the isolated ground.
You can buy a rebuild kit from CUCV Electric and you can buy an alternator off EBAY. I used rareelectrical and my original is being rebuilt for a spare sometime soon from the kit I mentioned which has better parts for the rebuild.
All this information is available many times over with a forum search.
EDIT- Does you Gen lights come on when you turn the key? They have to work for the alt to charge right.
GEN 1 and GEN 2 Lights. On all models except the M1010 Ambulance, generator lights come on when ignition key is in the “ON” position, but before engine is started. After engine starts, lights should go out and remain out. If either or both lights remain on after engine starts, press accelerator and let engine return to idle. If lights remain on or come on during operation of truck, IMMEDIATELY SHUT DOWN ENGINE and notify your supervisor. M1010 Ambulance has no generator warning lights.
I guess your supervisor will be your wife...honey I need some more money.