The peoples who populated Scandinavia at the time of your mod in the third century B.C.E. were not city builders. They lived in villages, hamlets, and farmsteads. Those who live in what is now southern Norway and Denmark were Germanic peoples. Those in Sweden and Norway belonged to a group known as the Finno Ugrians. None of these peoples had or were civilizations in the CIV III sense. They were not city or town builders.
What to do with them? I think that there are two approaches. If you want a strictly historical approach then you must recognize that there are portions of the map which will remain for game purposes essentially unoccupied for the entire scenario. Either close them off or populate them with barbarians. If on the other hand, you feel that historicity is not important and that the entire map must be populated for game balance or for some other reason, then by all means choose an appropriate representative name for these proto civs. I would explain in the civilopedia what I was doing. For example, 'there was no civilization named "A" at the time of this scenairo The name "A" was chosen to be representative of the peoples who lived in area "X" in the "Y" era.' Scandinavians sounds like a good name.
Personally, in an historical mod, I would do everything I could to veer away from anything which might smack of fantasy.