Hi Ken, thanks for that!
I ended up picking up some Rover blades this morning, and strangely enough the holes where the existing blades were mounted had half flats so they fit perfectly!

I also threw in a new spark plug to replace the old fouled up one, and pulled apart the carb/fuel tank assembly and cleaned 20 years of grease and grass from it all.

This thing seriously runs like a new mower! So much more power now, and a much much cleaner job, and now the clippings actually go in the catcher and not all over the lawn smile

Thanks for all your help guys!