Mate,
If you visit the Australian War memorial site and search for the 3.7, you will come across a couple of photos of a mobile mark 3, being used in the ground role with 25 pounders, and matilda tank, in Tarakan

http://www.awm.gov.au/collection/108894/
http://www.awm.gov.au/collection/108890/
http://www.awm.gov.au/collection/108887/

The reason quoted why the 3.7 was not used extensively in the Anti Tank role as was the 88 was that plenty of capable 25 pounders were readily available. The anti aircraft threat/role therefore received higher priority.
Other factors, smaller detachment for 25 pounder, thus more guns can be fielded.
Time into action less for 25 pounder and yes in a pinch it was possible to unhook and fire both types without coming fully into action but again the 25 pounder had the edge.