magneto small adjustment to custom extension, show product qty value in two admin grids

I have created a small Magento extension to add columns to the associated product grids within the admin area when viewing grouped and configurable products. The extension used two files and extends /app/code/local/Rebel/Adminhtml/Block/Catalog/Product/Edit/Tab/Super/Config/[login to view URL] /app/code/local/Rebel/Adminhtml/Block/Catalog/Product/Edit/Tab/Super/[login to view URL] The extension adds a grid column showing the product photos for associated products for both product types. I need another additional column showing the product stock level qty value that can be sorted and filtered. I will provide access to my development server where you can adjust files to complete this project. I will need to know which files are edited so i can replicate it on my live server. I found this code which seems close to the solution, but I couldn't get it to work: added to protected function _prepareCollection() ..... ->joinField('qty', 'cataloginventory/stock_item', 'qty', 'product_id=entity_id', '{{table}}.stock_id=1', 'left' )->joinTable('cataloginventory/stock_item', 'product_id=entity_id', array('stock_status' => 'is_in_stock')) ->addAttributeToSelect('stock_status');