Hey Letharion, I have an image file I used for a box set mockup/gift I made for my players which you can see here.
https://itch.io/t/2561050/heroes-of-adventure-box-set-pics
It shouldn't take my very long to tweak this box set image size as a one-off.
Do you know what dimensions everything works out as? (Cover, Spine and Back Size)