Too cold to go outside right now, but all 94-04 V6 Mustangs, Saleens and Mach 1's with the running pony emblem are the same size. So any of those cars will have what you are looking for.
For 2006, Ford started the pony package V6 Mustang which came with fender pony emblems like the older V6's. Same design, but the emblem is MUCH larger. Maybe this is what you got.
How many posts are on the backside? Should be a large center post and two alignment posts on top and bottom.