Frank,
The only Alison bunkers I've seen, unfortunately, have been at Sea Island and Timber Point.
In both cases the overall shape of the bunker itself wasn't anything particularly fancy, but as Tom Mac mentioned, they tend to be on the large side in terms of overall expansiveness and mental impact.
Also, and perhaps more importantly in my mind, they were sand-flashed up to the top, with fairly steep faces, sometimes with an overhanging grass lip that almost seemed to defy gravity. The bunkers were generally long ovals, often cut into rising slopes, and in the words of some great architect, sometimes seemed to cut into a green's very innards.