G'Day David and welcome to this great Forum.
What a great find and it actually runs, you won the lottery fella. Sounds like it is now up for a good service so this is what I did to find replacement filters.
Take note of the engine make and model and serial number/s if any.
Take the filters off and measure them by the OD, ID and length and write a description of where that filter came from, fuel, oil, air.
Then I rang my local supplier of filters and oils, and after a brief discussion I emailed him all the specs. The next day he had everything worked out and cross referenced for the engines I have and the tractors and truck.
Sometimes these suppliers have the information at hand, it is just sometimes if you have a counter jumper that has no interest he wont help.
Someone here will help you date your engine as there is 2 ways of dating Listers and I am not familiar enough with how it works. Maybe try a search on this Forum for engine dating.