Had this similar problem on my friends 68 Roadrunner after we broke in the 383. We were hearing a loud squeeling at the front of the engine. Well it turned out that the the new bolts that were used to mount the pulley on the crankshaft, were too long causing the bolts to scrape against the timing case cover. We put in the correct length bolts and no more squeeling. This may or may not be causing your problem, but it's something to check.
