In perfect tune a stock B18 will produce emissions that are at LEAST one hundred times greater than a new Honda or equivalent. There is no way you can clean up an old car, and the idea that using an old car is somehow environmentally friendly is ridiculous. We drive them because we love them. If your love of the environment is greater, then buy a new car.
CO emissions on older cars are held to about 2%. A B18 would be hard pressed to meet that, but can. New cars - .005% maybe? That's a huge difference. Hydrocarbon emissions from SU's, and you know how much I like them, is a joke. Nitrogen oxides - same again - a joke.
Keep in mind that modern cars emit fewer emissions, about 1/25th as much, as a lawnmower.