Thanks again Geoff and David.
Was looking over my folder of collected images, and it seems the aerial atop the extension located hull side was pretty much standard. Though did come across one photo that did not make use of the extension.
For the aerial on the front glacis, those with the thicker bottom stem seem to be present during first month or two of the Normandy campaign and only on the M10. The Achilles photos have on the front the simpler set A utilizing Base No8. They also seem to be located in one of two or possibly three locations on the glacis.
The colour photo below shows two pot locations but period photos only ever show one aerial ever being used on the front.
As for the M10/Achilles being a command vehicle equipped with two radio sets, it is not mentioned in the War Establishments. There was instead Universal Carriers used by troop commanders. These would be replaced with tanks were made available as Observation Posts in the form of Valentine or Crusader AA.
http://ww2talk.com/index.php?threads...tillery.23770/
Anyhow lots to chew on, thanks guys. Now on to find better detail images and hope to find some dimensions.