It's been some time since I did the upgrade, but what I recall was the collector is the same, down to the part number. I looked carefully at the time wondering to re-use the stock collector or use the new since the stock was in good shape. The stock up pipes slide in with the donut and then the clamp around the donut. The donut can get loose and cause a leak. The bellowed pipes aren't really bellowed but have the same idea that the pipe slides into the collector and then there is a flexible tube welded around the up pipe to the flange that bolts to the collector to hold the pipe in place. Since no donut is necessary, a flat metal gasket is provided to help seal the collector to flange connection.