Add Inventory column to Products Ordered Report In Magento

Hello, I would like my reports/products/products ordered report to have an additional column that shows the current stock of the item. I would also like it to them subtract Quantity Ordered from Stock in and the result in another column. I would like this code to be in the local folder so it won't get written over when upgrading. So the layout would look like below, where the last two columns would be the additional programming from stock code: Period Product Name Quantity Ordered Stock Q-S Mark