Very hard to date silverplate pieces with any certainty as they did not get struck with a date letter (unlike British sterling). Periods of operation, periods of use of different versions of marks, style, are your best indicators. Also, it is EP without a doubt - there is no Lion Passant etc to sign...
It might be worth writing to the Silver Society of Australia with your query - they are quite helpful and have a number of authors published on Australian silver among their members
I agree with Bahner. The engraving would appear to be designed to capitalise on the purported "providence" of a piece related to the German flying ace Max Immelman.
Both HH and HBH were marks used by Harrison Brothers & Howson. I quote "Originally known as Harrison Brothers (from 1849) this Sheffield manufacturer took on Howson as a partner in 1862. The majority of flatware produced by them was EPNS, however some silver items can be found. They also pr...