Why the huge PS Reservoir on Pete 359?

Okay, dumb question but I've gotta ask... why did Pete put the huge power steering reservoir on the 359 (or any other truck for that matter)? You know, the one bigger than a Lubrifiner but smaller than and air cleaner. My intuitive guess is for added cooling and fluid capacity for regional, off-road or city trucks. If I'm wrong, I'd like to know. Real reason for wanting to know is because I'm converting my 359 to dual air cleaners and I have to change the PS reservoir to a small one that fits under the hood. Are the pumps the same or am I going to get myself in trouble without other changes?

Thanks and Happy New Year!

 

So I'm pulling the huge reservoir to fit dual air cleaners. Question is... to mount the small PS reservoir, does it have to be above the pump like a car's has to be? From all the photos I can find, 359s with a 3406B mounted them on the engine up high and W900s with the same motor mounted them low on the frame rail.

Any old techs out there know if I can mount it high or low? Was the PS pump on a KW different than the one on a Pete? Thanks for any help. Here's pictures of what I'm referring to. Pete on the left, KW on the right.