One thing to realize is that a regulator in a TO-3 can will get to the same temperature ( all other things equal ) if it is rated at 1.5 amps or 3 amps, with less than 1.5 amps. So, putting an over rated regulator is just costing more money that could be invested in a better heat sink. In fact for a S100 card, you are more likely better off putting two regulators on the board with the 1.5 amp rating than one 3 amp one. Another point is that it is better to put them on different ends of the board because the slight drop across the board will help them share the current load better( some RAM board designers never got this ).
Also, check the heat sink's designer recommendations. Changes in orientation can make a difference. The one used on this board was likely the worst from what I recall but it is only a small difference.
Dwight