Recalibration using the Apple Service Diagnostics 2.5.8 brought the dual 2GHz machine's CPU temperatures (after new heatsink compound was applied) down considerably. Presently operating at about 48-53ºC (CPU A) and 42-44ºC (CPU B) . That is pretty good.

The machine HAD been previously calibrated with the old heatsink compound in there. I had not thought another calibration was necessary, as I hadn't swapped the processors. Evidently it is necessary with any change. One learns a little every day....