I certainly remember seeing a few of the YM226 models over the years. A machine from '81 has surely put in its fair share of work by now. It's essential to know your tractor is a "gray market" machine, meaning it was not initially built for sale in America. Are you looking for general information or trying to solve a specific problem with it?
The Yanmar YM 226 is a good little tractor, but honestly, it's so old that most owners today are restoring rather than using it regularly...finding parts and manuals can be more challenging than you expect.