You are pretty safe with Bren LMGs in Tobruk. Rifles were almost exclusively SMLEs (long Enfields) and few Tommy guns with both pistol grip and flat forends (both stick and drum magazines used).
Bren Carriers (early versions) were deployed by Poles in Tobruk in 1942. I think you can safely put one in Australian service in 1941 since British were using them in Egypt as early as 1939.
You can check some photos at my site
Hope this helps,