So, oddly enough I might be able to lead you to the right spot. I've since sold my blowthrough carb'd 85 coupe (several years ago now) and bought a Procharged C6 Vette to replace it.
Come to find out, that really annoying belt squeek is VERY common in the blown C5/C6 community. People usually get the "cold chirp" then once the belt heats up it goes away. I assume this is what you have as well, as your mod motor is the same basic serp setup as my LS2. The cause is simple...pulley misalignment. One, or more of the pulleys is just a bit out of alignment. Your best bet is to have a shop, or buy the tool yourself, laser align the whole setup.
In the case with my car, Procharger F'd up when they initially did the brackets for the LS2's. After some temp fixes I went with an aftermarket vette shop's bracket setup that cures the belt misalignment. Turns out that after I swapped the brackets over the chirp remained, and horrific belt squeel joined the party! After taking it to my tuner, it turns out the issue was something really stupid, the blower pulley had been installed backwards when they did the last pulley change! I ran a Novi setup before on the mustang so I didn't know that the Procharger stuff was spaced differently on each side of the pulley......anyway, something to check.
My old car:
1985 GT with T-tops. Sportsman based 342, AFR 205's into a Vic Jr. and a C&S Billet Aerosol 800 carb fed by a Novi 2K, MSD Digital 7531. Street tune is 582rwhp at 6500rpm . Tube K-member and arms. Built 8.8 with 9 inch ends. Cage and chassis work by DMC Racing. Tuning by SD Concepts.