I was searching for some info with no luck on what size the star bolts are on the alternators. Even with a chilton's online DIY subscription I was disappointed it didn't have that info, in fact it was poorly done, with some pics of an old generation if even an F body?
So, I'll put this in a basic format, so even if all you are wanting is the size for the bolts here it is. Maybe pic's added at some point if I have more time.

First disconnect either the positive or negative terminal on the battery. Careful as you do this that the wrench doesn't hit the other terminal, or something metal as you wrench on the postive side.

Next take a breaker bar (socket type bar, NOT a prybar), or a long wratchet to turn the tensioner to twist it to loosen the belt. On mine it was counter clockwise about 1/4 turn, then easily slip the belt off the alternator, don't need to take it all the way off, easier to see the routing and replace if left on the rest of the stuff.

Next you might want to unplug the connector on top of alternator.

The star bolts are a pain.
I got a centurion brand (cheapo quality) T40 size at osh, and it just twisted in the upper alternator bolt. Next trip was to get their craftsman brand at 6.99 each, wich worked much better. But, first i had to soak the bolts in wd40 overnight, don't accidently overspray on the belt and pulleys as I did (easier to cover them with a rag before spraying), if you do clean it off with soap, or will cause slippage and or the rubber to degrade faster. PB blaster brand or GM is reported to be better penetrant. as the bolts are usually corroded stuck. they still didn't want to come loose, so a hammer on them a bit can help break them loose along with the soaking in penetrant. you do NOT want to strip these. After those treatments they broke free.
ALSO, not great engineering, they made TWO DIFFERENT sizes for the star bolts, on the alternator. The top is t-40 size, bottom one larger t-50 size alternator bolts. Remove those two and the back brace which is a regular hex bolt. then slide back the rubber protector for the main wire that provides positive current on the back of the alternator. again a small hex bolt.
replace in the same manner as above with all steps in reverse order. start it up to make sure voltage is above 13v and all is good.
oh, and do NOT use a prybar on the tensioner. i did that once in a pinch, and it bent-twisted it, after which you get that squeeling sound, resulting in a several hundred dollar dealer visit to replace the tensioner. Use the breakerbar on that square opening on it to twist it.
keep in mind 12volt batteries are really not 12volts. more like 12.75, and if your alternator isn't boosting it to over 13volts, you will keep getting a rundown battery and dim headlights, slow working window motors etc.

 

Actron autoscanner with camaro firebird:
I'll throw an FYI in here, that may help if folks are doing a search function. I've seen several posts saying scanners don't work with the OBDI on the 3rds.
I have a cp9127 OBD 1 cable with cigarette lighter adapter with a cp9185 actron elite autoscanner to scan codes on a 1989 firebird. It worked just like it should. Make sure the ignition is on after connecting or it will just display can't communicate connect cables type messages. I have an EGR ses code being thrown is what I'm doing now that brings this up.