That motor could be either a G50 [187cc/5hp] or G65 [240cc/6.8hp]. Good in their day, but not many parts are still available for them - both are 1970's models. Both use an NGK B6H or B6HS spark plug, BTW.
Scans of an owners manual for these are in
THIS past thread.
Looking at the design of similar 'flail' scarifiers, I'd suspect that the motor relocation has been due to removal of a cutter clutch mechanism, in the engine swap process. Thus making the machine direct drive. That's something that the Elfin Safety authorities of today will disapprove of highly, along with the current lack of belt guarding.
There is a mob in SA who still manufacture a fairly similar looking machine;
http://powermowers.com.au/products/powermow-scarifierA lot of small local manufacturers of niche products, like turf machinery, did not survive the 1970's tariff reforms of the Whitlam government. Some did keep going longer, for example Alroh and MEY in WA until recently.
But with no manufacturer's marking/plate, it's probably not going to be possible to determine who made it.
