This has noting at all to do with the Pontiac GTO, but rather with the origin of the name GTO as applied to the Ferrarri GTO (after which the Pontiac was named).(posted 7979 days ago)Apparently, in order for a vehicle to be homologated (for european racing such as Le Mans), at least FIVE of them have to be offered for sale to the public.
The number 500 mentioned earlier had to do with NASCAR in the late '60's and early 70's when cars like the Superbird and Talledega ruled.