The plastic cupped Stronglight headsets that were used on Treks in the 80's weren't really bad as some might suspect them to be as I never ever heard of problems with them cracking or breaking up under use (except maybe in case of a bad crash). Remember, the plastic cups do not really take any wearing loads as there are separate steel bearing races in the headset that takes that. In the end, if you do want to use a non plastic cupped Stronglight headset, you can't go wrong with the aluminum cupped A9 and the Delta as they are pretty much the best designed headsets in the 80's.
The Miche Primato needle bearing headset is also a good one and a good value to boot at only around 40 bucks brand new. Pretty much a direct dopy of Stronglight designs. I have one on one of my bikes and it has never given me any problems yet. Its aesthetics look a bitmore modern than the Stronglights and will look nice on later 80's bikes with aero themes on it.

Chombi