At random times under hard acceleration my belts have a tendency to screech. Not sure if it is too loose, too tight, or what but its embarrassing when you put the hammer down and the screech is almost as loud as the exhaust

Generally a loose, old, or mis-aligned belt. Either replace, or if new, try rubbing some bar soap on the belts.

Check the width of your belts. The power steering pump belt is a 1/2" belt and the alternator is a 3/8" belt per the parts ID list. When I bought my car it screeched under hard acceleration. I looked at my power steering pump and it was a bit out of alignment. The more I got it in alignment, the more it squealed. I looked a bit closer and noticed the pulley grooves were different sizes but it had 3/8" belts on both. I looked it up in the parts illustration list and it was supposed to be 1/2" on the PS and 3/8" on the alternator. I just assumed the owner made a mistake and it was a quick fix. Fast forward a few years and I was working on my buddy's '69 and he had 3/8" belts in both. I pointed it out and he said he had just replaced them a year prior and that's what the store provided. We looked up the belts on a few of the chain parts store's websites, and sure enough, they were calling out the wrong belt. I'm not saying that this is indeed your issue as a handful of things can lead to this noise, but if you have the wrong belt, you'll never make it totally quiet.

^^^^This

Most parts store sell belts in metric sizes 15xx something. 15mm falls in between 1/2 and 3/8. The easy fix is replace the PS belt with a 17mm. I tired the gates 1/2 and 3/8. My Alt belt kept flying off on hard acceleration. I have not had a single issue with the 15 and 17 mm blels.

hmm 15mm is larger that 1/2" are you sure your saying right size? 17 mm is getting close to 3/4"

I can get a better pic tonight if you like. My brother has done this on his cars too. No screeching or thrown belts. They will ride a little high on the pulley but they work well.

Awesome help thanks. I looked up part number online and it specs 1/2" went to pick it up and was only 3/8" not even size listed. So I matched the belt circfrence with a true 1/2" belt. Put it on throttled down screech gone

Thanks again

Glad that worked out for you. Not sure why the part shops have been selling the wrong belts to everyone.

May want to check the water pump, alternator and power steering for ease of rotation. If you have a bind due to a bearing or some other cause it may squeel on acceleration until the speed of the pulley catches up with the speed of the belt.
Just a thought

Here is a pic of my belts. The carquest belt is wider. I thought it was a 17xx belt. I might be wrong. The Alt belt was the 15xx belt. I tried to use the original size 3/8 and 1/2 belts that I got from Grainger. Gates has them. But the 3/8 is just to small. When I would rev the 455 it would throw the belt. You can see from the pic they ride a bit high but not excessive.

Thanks for clearing up the size. I read that the 15mm was in between but never verified.
1/2 = .5
3/8 = .375
15mm = .59
17mm = .669

Just remember, it's not just the width that you are looking to find an equivalent to, its also the cross section (height and angle) when moving from an original standard size to metric.