I always thought the twin wipers were an export/USA item as well Joe.
All the UK ones I've seen have had the smaller front side indicators, no rear wing side indicator lamps and a single wiper system. In fact until I saw photos of Europas from your side of the pond I didn't realise there was a twin wiper system. The parts manual should tie the switchover date; I have the TC one and that lists a double wiper system for the Federal TC, so presumably at least 1972, maybe a touch earlier ?
Brian