1983 Chevy 305 small block.
Hearing a grinding sound near the alternator.
Is this a bearing or something grinding near the belt ?
Not exactly sure how to diagnose.
The sound you are hearing is most likely the bearings going (gone) bad in the alternator.
As @resident_heretic suggested, removing the belt and checking the alternator by hand is a good suggestion. You can also isolate the sound by using an automotive stethoscope (can be bought at Harbor Freight for $5).
Even if you don't have that, you can isolate the noise by using a long, flat tipped screwdriver. Place the handle up to your ear (can even rest it on the bone behind your hear), then place the tip on the alternator housing and see if this amplifies the noise. You can touch it to other portions of the engine to see if the noise is there, as well. Be careful when doing this, though ... do not wear any dangling jewelry, ties, or loose fitting clothing. It's really easy to get this stuff caught up in the fan belt or other moving parts. Would pretty much ruin a good day otherwise.
I would bet, since you have a v-belt accessory system, you do not have a tensioner pulley or idler pulley on it. Those are pretty much relegated to serpentine belt systems.
Judging by noise alone.... Could be a belt tensioner pulley or the alternator fan (the little metal thing on the front of the alternator with fins) scraping on something. One way to test is to remove the belt and turn the alternator manually. It could also the belt itself. Hard to be sure just by sound alone.