use blog posts block design for regular content

You either need to have the books page HTML conform to the same HTML structure as the blog page, in particular the class attributes used; or add custom CSS so the current books page elements have the same styles applied as they are applied to blog posts.

Your browser’s element inspector tool can help you learn what HTML structure to use or what styles you need to apply to existing book elements. It looks like much of the styling is already the same. The main differences I see is the thumbnail sizes and font size are not quite the same.

For example, one way to make the font size the same is to add the following to the Additional CSS section of the customizer or style book:

.wp-block-uagb-container p {
    font-size: 16px !important;
}

If the above works without the !important, all the better.