Wow!! What a site, lucky me finding it...

Welcome to FABO, inertia, from sunny SoCal. You're going to have fun here!
You post brought back lots of memories of my old '69 340 Swinger. Like yours, bench seat, no headrests. I bought it used in very late 1969 from the original owner - he'd only owned the car a couple of months but had joined the Navy and couldn't keep the car.
I eventually built it to the extent I was driving a nasty-cammed 340, 850 Holley dp, reverse-pattern manual shift 727 and 4.89 gears on the street. Sure was fun back in the very early '70s. Raced it primarily at OCIR and cruised Whittier Blvd in SoCal on the weekends. Wish I still had the car today. Was building it to run NHRA Super Street but went through a divorce that stopped the build effort - being a single dad with fulltime custody of two young kids didn't permit any "toy time". Eventually sold it during a family financial crisis years ago.
Currently in build-mode on a "new" '69 Dart.
Post pics of your Swinger, love to see it.