Hi rotachoc,
Well the engine was manufactured at the Rolla plant in the USA on the 14th of August 1986 which makes this a November / December made mower if it's the original engine, something which I'm still not quite sold on. I still feel that it's an earlier machine with a later engine put on it. I will make further enquiries and get back to you on this point.
As far as the reliability is concerned these engines were very good, maybe not the smoothest but most certainly a good long time runner if correctly maintained.
Cheers,
BB.