DaleC,
Ivor is from Scotland and moved here to Australia before moving on to New Zealand. He lives in Palmerston North. He was a mate of Ted Eldred's, along with Bill Young, back when Ted as still working on rebreathers. Ivor is a member of the Historical Diving Society SEAP. He and Bill Young were the first to dive Heron Island which is about to have it's anniversary of diving. They dived it in November 1953. He had an early "tadpole" Siebe Gorman. They used twin 26 cu ft tanks. The tanks were inverted with a reduction valve at the manifold, and the double hose demand valve behind the diver's neck.
He recently sent me a copy of the syllabus for the first diving course offered in Australia. They taught rebreathers (O2 and EAN60) as well as with the Porpoise. All three were on the certification and they drew a line through the ones you didn't do. His course was on Feb 12th, 1954.
When we did our recent vintage scuba course we included rebreathers because they had. W also used Porpoise and other single hose from that era, as well as the double regulators.
I am sure he would be happy to know you enjoyed his little book. He doesn't get out much now as he is his wife's caregiver. Steve