With those dropouts, I doubt it is much (if any) later than 1950.

The lugs are also totally unfamiliar to me, but from the little I've seen of old Australian frames I'd bet that's what this is. I don't think it's a Malvern Star, but something similar. The raised letters you mention on the bottom bracket shell are not a serial number, but rather part of the casting. The builder bought basic frame parts (lugs, dropouts, etc; probably all of English make) and filed them to this distinctive shape. My advice would be to show more photos to us and to the guys who collect old Australian bikes. Maybe post the pictures here:
http://www.bicycles.net.au/forums/viewforum.php?f=23

Whatever it is, it is a great find. Congratulations!