My only recollection of a "nine bob note" was in the saying: "as bent as a ...."
Being a reference to a homosexual as they were both illegal back then.
Combustion engines are always quoted in displacement of cubic centimetres yet [for older engines] the bore and stroke were in inches.
E.g. the famous Rolls Royce Merlin was 5.4" x 6" [B&S] giving 27 litres aka 27,000 cc
As an aside, the Merlin was a v12, weighed 600kg and churned out just over...