First, thanks to all who offered suggestions and support. It all helped.
I did the job in the water. First I had to disassemble one and measure, reassemble and run to the store.
My boat with a 2" shaft uses 3/8 packing. The WM store had a chart of packing sizes they've encountered and the 2" shafts generally take 3/8 or 1/2.
I pre-cut the packing to save time. The worst part of the job was picking the old packing out of the nut while the water was running.
I got both sides done in pretty short order and all is good. Perhaps 1 drip per minute. I can live with that. After I run them in and re-tighten them it should be a job well done.
As a side note, the bilge pump cycled 14 times during all this. Not too bad.