I know nothing about the rotary hoe, aussietrev, but here is the IPL for the engine:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6kpuAVJ1DajI.pdf

Here is the Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/flhsuIX-nfBhU7y.pdf

It was made on 10 March 1978.