White smoke from 280 sel 1972
 

what does white smoke mean from a 72 280 sel at start up?

Hard to say with certainty but the transmission vacuum modulator is a good place to start. After the vehicle sits overnight, loosen the vacuum line to the modulator to see if transmission fluid weeps out. Mark

Smoke on start-up is a classic symptom of worn valve guides / stem seals.

Next stage in the progression is for it to smoke badly when you drive off again after coasting to a stop.

If it's only on start-up, you can probably drive like that for a long time.

I agree that checking the modulator is a good move, although a modulator would usually smoke at idle even when warm, and you'd notice a pretty heavy ATF consumption.

A small wad of cotton or cigarette filter placed into the rubber elbow connecting the intake manifold to the transmission vacuum line will indicate if you have a leaky shift modulator. It will turn red. Probably don't want to leave it there for longer than needed to test that.

Sometimes some upper cylinder lube will free sticky rings and restore the seal. Worth a shot before you tear the engine apart.