The rear end code should be something like "C BS 0820 G2" with an "E" for Eaton underneath if it's a posi Eaton which yours wouldn't be (non posi). That's for the late 69 rear end. I attached a pic of mine.
I can't imagine a 69 Z28 ever being ordered without a posi.
From CRG:
http://www.camaros.org/drivetrain.shtml#AxleCodesAxle Code Format: aa mmdd fs
p
where:
aa = application code - two alphabetic characters
mm = two-digit numeric month (01-12)
dd = two-digit numeric day of month (01-31)
f = factory plant code
G - Detroit Gear & Axle plant
s = shift code (1 or 2)
p = a positraction manufacturer code, when applicable,
is added on a second line. The posi manufacturer
codes are D for Dana, E for Eaton, and W for
Warner.
Example: BL 1122 G2
For a 68 or 69 model, this is interpreted as a
3.07:1 axle ratio, non-posi, 12-bolt rear
axle assembled on November 22, 67 or 68 by the
Detroit Gear & Axle plant, second shift.