You didn't mention that it is a Kirby engine, roebuck, which was making it unnecessarily hard for us. The names of quite a few of the Kirby-Lauson engines had a simple code. H meant horizontal crankshaft and V meant vertical crankshaft, K meant built, assembled or sold by Kirby in Australia, and the number at the end was the alleged gross horsepower in tenths of a horsepower. The HHK range included, at a minimum, the HHK40, HHK60, HHK80, HHK100, and HHK120. Hence the HHK100 seems to have been alleged to have 10 hp gross output.