Any ideas whether a 1973 Simca 1100 can run on Super Unleaded as it is the same 97 octane rating as Four Star or whether you need to use additives, if the car hasn't had any kind of conversion?
As the Octane rating is the same, the performance will be the similar.
The head however, is not modified, (hardened seats etc) and therefore additives might be a good idea, (valvemaster or similar).
I just noticed you are one of the UK members, so a check with the technical department of your chosen fuel supplier might not go astray to get the specs of the fuel. (i.e. do they already put in a lead replacement additive/valve set lubricant).