power valve block off

IMO

Yes you should install them. (Simple Explanation) They work off vacuum and aid in provide the fuel that helps idle and drive-ability at low RPM's. Figure out what came stock on the 750, and work from there. It's based on engine vacuum so you need a Vac guage. While your in there, I would check the jetting as well. Hook up an A/F gauge, if your able too, so you can tune it properly.

Here is a link to some basic info on set up and how it works.

Choosing the Right Power Valve for Your Holley Carburetor

Good luck