So was changing out my alternator for a more higher output one. And was tightening down the bolts for power steering pump and ran into a problem as this bolt won't get tight:

All the other bolts that hold the power steering pump are tight. While this is sung but not tight since if i tighten it more it spins and becomes loose.
So would it be ok being sung? And if not does anyone know what size tap i need to use to rethread the threads for the hole? And if not would a longer bolt and a nut work?

If it’s spinning it’s done. I would use a longer bolt with the same threads and a nut. I don’t think you have much choice at this point.

I concur, very easy to get a nut behind there. However, on mine, I found that a previous owner had put the wrong fastener (metric/SAE or SAE/metric) into that hole, and the bolt was short enough that it only damaged the threads in the front of hole. A longer bolt of the correct diameter and threads size, threaded all the way out the back of that hole, was able to hold sufficient torque. I didn't expect that and had a nut standing by, but did not need to use it.

Agreed. Its either that or cut some threads for a slightly larger bolt.

I need to replace the bearing on the pulley and figured it would be proactive to replace the entire power steering assembly as it is a 99. Which one is actually the best? By best I mean most dependable.

Cardone remans are pretty poor quality, and you'd likely end up with something worse that what you're replacing. Personally if it ain't broke, don't replace it.