Usually here in the US we can date them by a triangle shaped safety decal that is applied to all power equipment in the 70s-80s. The decal has info that includes the date, however that decal is missing from mine. Mine does have the Tecumseh two-cycle engine and I believe needs only a spring for the carb/governor to run. I plan to restore it eventually.
I have looked for years for a blue Flymo, without success. I have been told that blue ones were never imported to the USA, possibly Canada. I’m not sure if that info is correct though.
I talked to a local small engine dealer, now deceased, who told me that he once sold Flymos and after a year of no sales he saved only the Tecumseh parts that might fit other applications and hauled a large truckload of new Flymo parts to the landfill. Wish I had been there. I would have been glad to save him the trouble!