The following will add new fields to products table. When adding new product you will be able to enter length, width and depth of the product.
Adding these fields to the products table means that all products will have to be re-entered with the aditional three values or updated on the oscommerce.sql file by hand.
If you are working on a new shop this contrib' is easy to implement.
After applying the changes you will be able to control the display of product dimensions in Product listing configuration group.
If one of the dimensions is missing it will not show.
If all dimensions are missing you will not see the "Dimensions" heading in product_info.php page.
I can understand why this type of modification was not done by now because of the changes to products table.
If you can live with that you will be able to use the extra inforamtion for other purposes like shipping.