Goal post isn't here, but a small bar. You can see a connection for an aerial (cable) leading off this bar heading in the general direction of the main mast.

It's dated 1945 in japan I think unless another photo comes out of a closet somewhere, this will be the clearest yet. Would love to see the contact sheet this picture came from though!

To answer the other question regarding australian flags, there's only one Australian National Flag.
l.jpg)
The important part here is that the national flag used since 1911 and current is the same and has a 7 point federation star. The big star under the Union Jack. And all stars of the southern cross are also 7 pointed stars apart from the smallest which is a 5 pointed star.
The Australian white ensign wasn't put into use until 1967 so you don't need to worry about it. Commissioned navy vessels of the RAN used the RN white ensign until this time from federation. The Australian red ensign is for use aboard merchant navy and private vessels registered in Australia. During ww2 both the British red ensign, Australian Red ensign and Australian Blue ensign where flown by the mercantile marine (this is far more complicated story than the white ensign)
The only other ensign is the light blue variant used by the air force known as the australian Air Force ensign. Any other flags are state or territory flags and the Aboriginal and Torres straight islander flags.
_________________
AT
1/72 Arleigh Burke flight iia
1/72 Hobart class AWD HMAS Brisbane
http://www.shipmodels.info/mws_forum/viewtopic.php?f=13&t=1547671/72 Friesland
1/75 Wasa
1/53 STS Leeuwin II
1/72 HMAS Perth 1942
1/72 Russian Corvette Steregushchy