I found that I can insert both custom fields with one URL, so that part of my question has been answered.
When I add the product to the cart, the two custom fields appear on top of one another, like:
Product ID: 1081-17HT
Product Description: DISS Fittings; DISS Body Adaptors; Body Adaptor, Hose Bard with Hand Grip Collar; Carbon Dioxide
Is there a way to edit the cart itself, so that these two fields appear next to each other? Basically, I want to replace existing columns in the cart (image, product name, price) with the custom fields Product ID and Product Description. Is this possible?