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The castor setting is non-adjustable on the 1200 and on many other McPherson strut cars.

This doesn't mean that you cannot change the castor. You can, by cutting the tension rod bushing and tightening it up again. Or by re-threading the tension rod so it can be shortened up.

After doing this, the aligment must be re-checked (that is, the toe-out setting).

Castor is what the trolley cart at the market has: The angle of the wheel hub, so that the wheel tracks straight when the cart is pushed ahead. Datsun 1200 has minimal castor for a light steering action. But it is too light and does not track well at highway speed. More castor than stock is better. 2-3 degrees has been recommended. 4 degrees is the most I've ever heard of for a 1200.