You can fly a G-reg on an AUS license but do keep in mind the restrictions: all the restrictions of your AUS license apply, plus the restrictions imposed by the UK ANO on sucn an implicit validation (from memory: private flight, day VFR only, but LASORS will have the details.)
Endorsements, ratings, qualifications and so on are a touch subject in cases like this. Before you know it you're building a house of cards that may come crumbling down if even the slightest issue goes wrong. But in your specific case: under JAR there is no formal endorsement for aerobatics. Essentially anyone with a shiny new PPL can jump in an aerobatics plane and start doing loops, rolls and so forth. Not that this is recommended practice though - best to get proper tuition.
When I got signed off under club rules to fly solo aeros, my instructor wrote something to that effect in my logbook. It was not a legal requirement, but felt good anyway.
At the end of LASORS you'll find some safety sense leaflets as well, and I think one of them is on aeros.