Hi John,
Thanks for the additional info,
At a guess I'd say your mower was assembled around April ~ May of 1978 as the engine was built on the 19th of December 1977 and one must take the Christmas shut down and shipping from the USA over to Australia during the Christmas period into account. I'd strongly argue that the engine probably didn't even leave the USA until early 1978. This ties in with the sticker ID that was started around late 1977 and also that it's an Apple Green coloured machine.
I could quite easily become attached to this machine but not the Rover.
Cheers,
BB.