They are the same as the US versions for decoding, other than the second last digit (8 in this timeframe) is GMH spec, the rest of the numbers mean the same thing. That carb should should be 7029282. It is the most common HK-HG Quadrajet, from a 308 auto late HT or early HG.
The initial reason we got Australian "8" number on SBC engines in this timeframe is the US went to mandatory AIR spec for 1968 model year. GMH had already ordered the carbs for the GTS327 as a standard 1967 pre-AIR spec carby (for 1967 327/240, 327/275 and 350/295), and Rochester built them as 1967 spec using a 1968 body. Prior to the GTS327 the 1968 Impala and Parisienne that GMH assembled used a standard 1968 AIR US spec carby. For a long time all the GMH carbs after that including the final GTS327 carbs are unique Australian numbers, especially 308 as the 308 carb is not the same tune as a US vehicle anyway. Once Australia got the "clean air" ADR26 which is similar to AIR the HQ 350 engine went back to a standard US spec carby, but the 308 stayed as unique.

It is amazing how cheap all these carbs still are. Every swap meet I go to I pickup a few GMH numbered carbs, picked up two this morning at Morisset swap meet: an early 1974 HQ or LH auto carb and an 8th month 1977 early HZ or late LX (A9X) carb, for $25 each. Last year at Morisset I picked up a late HG ZB (same as the subject of this thread) and a post 1/75 HJ carb for $30 each. Morisset is also where I picked up a HT GTS350 carb and a big block tune US one as well. Didn't see a single one at Cessnock swap yesterday though.