Thank you very much for your inquiry. Here is the floor plan view of that space. It looks like this room is about 4' wider than your space.

The cabinets are 78" wide.

I have about 49" to work with for the bookcases. I love the way you divided yours. Can I divide mine the same, even though they are narrower, without looking skimpy?

Here is the cabinet layout with dimensions, hopefully this will help you with the scale of your project.

I would think that you would want to divide the 49" span for support, depending on what you are planning to put on the shelves.