Quickor and AddCo both make rear sway bars for early & late A bodies.
I installed a Addco rear bar, the 'street' (smaller dia.) on my '68 Dart over 20 years ago.
The entire setup has lasted and performed well for me.
The bar bolts to the axle with brackets and you drill and bolt brackets to the frame for the bar-end attachments.
I will get the heavier version for the convert.