Buy a GM 10-SI alternator. 1 wire or 3 wire is your preference. 1 wire style is easier to wire obviously but does have some drawbacks. Google “1 wire vs 3 wire alternators” and you will get many articles to help make your decision.
The biggest difference, in my opinion, is you can’t install an idiot light. I have a 1 wire alternator and while testing some electrical systems I have inadvertently left the ignition on and came back to a truck that would not start. I burnt out the coil and the points. If I had that idiot light, chances are I would have noticed the ignition was still on before I left the truck.
You may be able to buy an alternator with a 5/8” pulley but I had to change mine. I bought the pulley from Speedway. Easy to change, just use an impact to remove and install.
You will also need a new bracket to mount the alternator. I bought mine from The Car and Truck Shop and it needed a minor alteration to fit. The slotted holes were slightly smaller than the 3/8” bolts that attached it to the engine block. I sure you can buy one that fits.You will also need the bolt that attaches the alternator to the bracket.
