[Barnsnake]

According to the Mustang forums, that is a 1981-1985 50 oz. wheel for a 5.0 Mustang with a 10" clutch. If it has an additional number stamped into it (something like E6ZR) it is for a 10.5" clutch used from '86-'93.
The pictures on those forums show lots of balance dimples drilled into the weight. One that was well pictured had 13 "holes".