LOL ... I couldn't get to that site from work but I found it on Google .... make sure to download the measurement kit before ordering custom size!
Technically there is no such thing as a 1969 Shelby Mustang chin spolier. The chin spoiler wasn't offered on the 1969 model. The chin spoiler was added in the 1970 model year which was actually unsold 1969 Shelby's updated and assigned new VIN numbers by Ford and sold as 1970 Models. Along with the Boss 302 type spoiler they added twin black hood stripes.