[Mike V. Florida]

Originally Posted by johnbuckley

Great Britain offered the smaller bore size because of the road tax system in place there at the time. (though the 3285cc engine in cars was also available as an option). The smaller diameter bore brought the fiscal horsepower rating of the car in at 14.9hp, the larger diameter gave a fiscal hp rating of 24hp and attracted a higher annual tax paayment. This tax system was meant to favour the UK vehicle home manufacturing industry ( think small engined Austins and Morris). But in fact it shot the Uk industry in the foot as their cars became less and less suitable to export. The larger bore Model A engine was used on commercial vehicles in the UK which had different tax regime.
The smaller diameter bore engines of the Model A were GB specific though a few obviously made it across to europe and the empire countries.

So the original AF stamped engine Rowdy states he has is most likely a commercial engine.