Prolly the stockers. The only way you're really going to know is by finding the date code, usually looks like "EXXX" or "DXXX". The letter indicates the decade, while the first X would be a number showing which year. For instance, a part with "D8xx" would be a 1978 part. Unfortunately, if I remember correctly the date code is on the part facing the valley.
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Capri306, Moderator, The Mustang Works Online
1979 Mercury Capri, 5.0L -- C4 -- 2.73
1987 Mustang LX Notch