So, to close out this thread, I found some good information here:
http://rmcavoy.freeshell.org/starters.html
In a nutshell, shims can only be used on engine block mounted starters. Since the 307 starter mounts to the bellhousing directly, shim is not possible.
So, back to my original question, does this starter sound ok? The only option if not us to replace it with another. But I'm starting to feel like this starter is fine.