Assuming all players will actually be starting gameplay in the Ancient Era, and that the player will be building new cities (ie, you aren't talking about pre-placed cities already on a Worldbuilder map), you can add or redirect to have this as part of the definition of the building(s) under the <Buildings> table:
Code:
<FreeStartEra>ERA_ANCIENT</FreeStartEra>
You would just update each building that you would want placed in all cities always and add that tag to the building.
If you are talking about pre-placed cities on a worldbuilder map you either have to add all the buildings to the cities manually as part of the map (ie, in the city create/edit tab of WorldBuilder), or you would have to add all the buildings to the cities for all players via lua.
For lua methods I'm not sure if the GameEvents.PlayerCityFounded event fires on placing each city 'into the game' for a WorldBuilder map, or if it would be necessary to try to use LoadScreenClose.