For 60 euro you can get a heritage certificate from Citroen Conservatoire that will contain the ‘Date of Commercialization’ basically the date it left the factory confirming what you need for the DVLA
You can also get festoon bulbs for the trafficators that ‘flash’ when the bulb lights up so no additional lights and wiring are required if you want to keep the car as standard as possible. Not as good as proper flashing indicators though but a potential compromise to consider