I can't speak for your Swinger, but I bought and installed them in my 68 Barracuda, they fit in the stock holes with no modifications, I did have a casting issue with the one track on the passenger side, it was missing the tab where the seat adjuster spring connects to. Due to time issues with the work on the car I didn't have them replaced, so my passenger seat is no longer movable, don't like people in the back seat of my car anyway, so I don't care. Other then that, I did find them to be good quality for being made in China.
If you plan to purchase from P.G Classics keep in mind they do not refund money for anything they sell, only exchange. If your in a rush, its faster to deal with them direct over the phone, then through Ebay.