OK I got home and looked at the photos of the plates you sent through (bigger screen than my phone).

The HZ plates you sent through is not stamped XX7 on the body plate, it is an Adelaide built commercial ute trimatic. The reason you have an L is because that is the sequence of codes for dates to match 1979.

D – 1974
E – 1975
F – 1976
G – 1977
H – 1978
I - is excluded because it looks like a numerical one.
J - 1979