It appears you've lost the outer ring of your harmonic balancer and have only the inner hub remaining.
Thus far it looks like a common FE-type harmonic balancer that was used on FE engines for over a decade. You could go several different ways with a replacement (OEM, aftermarket, etc). If an identical OEM replacement is what you're after, try giving Damper Dudes a call. On their website I see a couple of different single-groove C3AE harmonic balancers (one with timing marks, one with timing button, etc). A link to their website is below:
DamperDudes.net (Americas Largest supplier of harmonic balancers)