67 GT350 looks the same as the small block service piece but is stamped with the C7ZX prefix
67 GT500 engineering number stamped on the clutch should be a C7ZX (assembly line item-not serviced )
This is a example of a NOS Service Replacement part
GT350 is the small block clutch but with C8ZX
68GT500 same as the 67 but C8ZX
GT500KR could have either C8ZX or the regular Cobra jet number stamping as they were phasing
out the use of the "ZX" designation at that time.
69/70 used the regular production units. I can only assume the ZX units " internally" were rated for higher RPM use or extreme duty, externally they were the same as standard production. TheZX designation usually referred to Shelby production but also was used on limited production " Experimental Items"
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