It would be a better encyclopedia if the information was correct.
The only Boss with semi heads was the Boss 429. And there was never any Boss 351. There was Boss 302 and Boss 429 and only for two years, 69 and 70. The Mach 1 with the 351 was just that, a Mach 1, not a "boss"
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1993 GT/AOD
'93 Mustang GT