I'm not sure, on the lubrication plate it is stated that the maximum speed is 65 mph, so that would indicate a kph dial.

I had a look at other speedometers of Harleys on the internet and I think this is a mph speedometer.

Perhaps not, but the maximum speed of these wartime HD WLA bikes was 65 mph (104 kph):
www.militaryfactory.com/armor/detail.asp?armor_id=511

HD had a bike (Knucklehead) that could travel at about 100 mph if wikipedia is to be believed:
en.wikipedia.org/wiki/List_of_fastest_production_motorcycles