Greetings folks,
That engine looks a lot like a Kohler to me.

Hermosil, a comprehensive set of manuals is free to download from http://www.allotment-garden.org/rotavator-manuals-free/
A better quality IPL is here: http://www.howard-rotavator-spares.com/manuals.php

The IPL says that a 2-ply 4.00-8 Ag tread tyre is the correct type. Here's a source: https://www.outdoorking-forum.com.au/tyres-tubes-and-wheels/cst-tyres-tubes?sort=20a&page=3
You'll need tubes as well.

Cheers,
Gadge

"ODK Mods can explain it to you, but they can't understand it for you..."

"Crazy can be medicated, ignorance can be educated - but there is no cure for stupid..."