Tapered valve guide and spring retainer assemblies are described for use in plunger pump housings that incorporate corresponding outwardly flared discharge and suction bores, as well as structural features for stress-relief. Plunger pumps so constructed are relatively resistant to fatigue failure because of stress reductions, and they may incorporate a variety of valve styles, including top and lower stem-guided valves and crow-foot-guided valves, in easily-maintained configurations. Besides forming a part of valve guide and spring retainer assemblies, side spacers may be shaped and dimensioned to improve volumetric efficiency of the pumps in which they are used.