That decal happens to Pontiac people, but it's a reproduction air cleaner decal that has its origins in Buicks. Too many Ponchos are restored with this decal.
http://www.ebay.com/itm/Pontiac-400-...-/230510581887
I don't believe there are any L89 convertible numbers but it's akin to the "1 of 18" LS6 ragtops.