I had a similar problem with my clutch assembly on my 1949 with a 261 over a 3 speed. As mentioned, two different throwout bearings but also differing clutch discs and the height of the disc hub. Gave me a ****load of problems until I got the right disc from NAPA. I documented some details on webshots in the album about the clutch. Never got the growl you mentioned but did find that the disc I got from a rebuilder was marked wrong between what was really the flywheel side as there was a distinct difference in the disc hub height. At least for my application.
http://community.webshots.com/user/geezer
