Make model market with specific equipment requirements.
Like make Norway market (Seatheat, foglight, catalyzer, electric window) required
French market (Aircon, power steering, electric window, rear view cam)
This will make two specific productionlines. perhaps with some basic parts of it combined with two outlets.
Car will only sell in market when meeting equipment requirements. Market has a limit selling value.
This will make it interesting to make several custom productionlines meeting different market requirements.
You can make a quest like progress in game with this. Constantly giving the player new goals, in form of markets appearing over time.