shelbygt500, doesn't look like a lot of the one you need are out there. The original 71 429 Mustang part was C8SZ-8546-D (Motorcraft YA-83) and was listed at 2 1/8". Might be a good ideal to check with Don (Ohio Mustang Supply) or Mike @ Motor City Mustang and see if they have anything used that might actually be from a 429 or something close to that size. The C8SZ was used on some 429 full size cars, 71-72 Police Interceptors, some Torino 429 applications, plus the sister Mercury versions.
The next closest size I found was a D1DZ-8546-A (Motorcraft YA-44) at 2 3/16". That saw a lot of use on 250 6 cyl cars with AC and 73/ 429/460 vehicles with the majority of them on the Interceptor models.
Give Don or Mike a call, they just might surprise you.