It depends on how accessible the particular plug is. There are rubber expansion-type plugs available that simply push into the hole, and a center bolt is tightened to expand the rubber and seal the hole. That's the simplest way to do a quick fix. If one plug is rusted out, the others are probably pretty far gone, also. I like to install brass freeze plugs on a rebuild, which don't rust out.
The length of the water pump shaft determines how the belts fit to align with accessories like power steering, air conditioning, etc. Different pulleys and accessory options determine what length shaft you need.
Jerry
