Good catch. You're correct the PS pump is stationary. I failed to mention the belt for the PS pump also drives the water pump and alternator. The alternator will be the tensioner for that belt.
1957 Plymouth (Hemi, Dual Quads, A833 4 Speed 9 1/4 w 4.10) Sold 1937 Dodge Pickup (Hemi, 6X2 intake, 46RH, Dana 60 w 4.56) Sold 1968 Plymouth Valiant 2dr sedan (354 HEMI, 46RH w/4.30 gears) under construction