Hi, thanks again for all of your involved help!
Unfortunately I'm still not getting the exact results I was orginally after. So when I created the new custom fields, I can see them appear in Additional Information as show in the following screenshoot.
Now with the new code you've given me, I can see these fields appearing in the Products list, which you can see in this image.
What I was hoping to do was have these custom fields editable per product, so in this case I would be able to have a text field for delivery_code to fill in and a tick the checkbox for delivery_confirm next to each entry in the Product list, apologies if I haven't been clear and thanks again for all your help!