I have some rebuilt 502's that are now 540 (ATECO did the work)
I am eating/shredding belts every week.....I spent a lot of time and money making sure all the pulley were aligned, that helped, but I noticed that maybe the NEW OLD STOCK Belts I am buying might be 20 year old belts and shredding themselves under the heat here in Texas.

Anyone have a good source or what the part number might be for a FRESH new serpentine belt?

The Merc/Quicksilver part I am referring to is :
57-861094Q

Once we made sure all the Pullies were aligned it did fix the issue or at least slowed the shredding part down, I am concerned that my issue now is the age if the actual belt is the issue.

The Merc belt on my 496 Mag was dusting and squealing. I read that the continental Elite belt would stop the dusting and squealing and it did at less than half the price of the Merc OEM belt.

That belt looks like it is 2649mm in length. I did a quick cross and the gates belt should be

K061037

Ran into this doing a quick search. One , of just a few, reviews says if you have a steel ps pulley on your 502mpi, this is the correct gates belt:

Found this on here (OSO);
Serpentine Belt Cross Reference for 502 MPI/454 MPI

Many thanks guys! Gates belt on order.....

Your alternator bracket is probably flexing at high engine speeds.

Will that bracket flex? It’s more like a box that the alternator sits in. Seems pretty solid to me.

If it is like mine it's just a stamped 1/4" steel bracket. I welded a support across the top of it and that stopped my belt from shredding.

Where did you weld it? Got a picture?