Hi Watson,

Here is your Operator's Manual:
http://bsintek.basco.com/BriggsDocumentDisplay/lrvvA-wU7eL7hAxB91ObQ.pdf

Here is your Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/Z6jmvGVJ1DajI.pdf

The engine was made on 18 July, 1974. Allowing shipping time to Australia, it was probably on a mower by the end of 1974.

It is 8 cubic inches displacement, or about 135 cc (the 8 cubic inch number is rounded). It is of the first design generation after Briggs adopted the modern model number system, it has a horizontal crankshaft and a Vacu-Jet carburetor, with plain main bearings, and a rewind starter.