Using titlepages with the `krantz.cls` class file

[friendly]

I have a book using krantz.cls style, and want to try quarto_titlepages with it, particularly to include a cover page, for which I have a complete image as .png and .pdf.

I cloned the repo, and tried example_1.qmd, simply changing the documentclass

format: 
  titlepage-pdf:
    # documentclass: scrbook
    documentclass: krantz
    classoption: ["oneside", "open=any"]
    number-sections: true

This generates an error: krantz.cls not found -- it is there under cls/. So, I copy this to the main directory and rerun. This works, but doesn't include the GreatWall cover page, which appears with scrbook -- and that is nowhere specified in the YML header for the example.

So, I'm stumped at how to use this for my purpose.