Hello Dave

Yep, a common Ironhorse https://en.wikipedia.org/wiki/D-400_engine
These were made mostly for Lawnboys and Masports.

Your mower was sold here between about mid-1970s and mid-1980s.
I'm trying to work out the exact connection with Vulcan, but I
think it goes like this.

Vulcan was/is a heater and hot water manufacturer.
They wanted to get into lawnmowers and they sold Masports and
Supa-Swifts using the Vulcan name: Vulcan-Supa-Swift and Vulcan-
Masport.

Vulcan is not mentioned in the definitive Jim Allnatt book on
Masport; suggesting no close connection between the firms, but a
commercial deal between Masport Australia and Vulcan at that time.

Hope this helps.
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Jack