Knowing the engineering of the time - I'd wager a bet that originally (like
a lot of old diesel and petrol engines) the size/ capacity was stated in
cubic inches.
This is an area in the UK where metric really has become defacto - engine
sizes. Usually expressed in litres or more commonly cc (cubic centimetres).
I know of no-where where cu in are used except in certain "hot rod" type
engines - but those are rather exceptional (and have a 'fan following'
rather than are practically used everyday).
Common sense would dictate that the cu in value was converted to 'litre'
(not even cc) just to cater for the fact that to 99% of Brits a cu-in figure
would mean nothing and leave the viewer with nothing to compare to (like
their own car engine size, for example).
* It¹s engines were designed and built with their capacities in litres.
