Only mention I see on the "Z":
Field e - interior trim code
The first three digits of the trim ("TR") code are a unique (for each year) interior color and type code that indicate the color and standard or custom interior.
1967 tags also have a hyphenated suffix that indicate seat and headrest type:
Z - standard A50 Strato Bucket seats (no headrest)
Y - RPO AS2 headrest added to the A50 bucket seats
H - RPO AL4 Stato Bench seats (no headrest)
T - RPO AS2 headrests added to the AL4 bench seats
From this page:
http://www.camaros.org/numbers.shtml