There was a site devoted to 69-70 Mach 1's called "The Mach Pit", but I haven't been able to find it lately. There is a site at http://www.69mustang.com that caters to all 69 & 70 Mustangs and that has a registry. Other than that, I'm unaware of any other Mach 1 registries.
Thanks for the compliment on my cars. /forums/images/icons/blush.gif