Layson's is the only place I have seen that carries the
square bushings for the early A sway bar. Admittedly, I have not done an exhaustive search. I just did an easy search. The link might work. It might not.
I just did this replacement on my 65 Barracuda so I will describe what I did. Your mileage may vary.
I ordered the 7/8 inch hole bushings (GG80c). How did I arrive at this size? A 7/8 inch wrench barely fit over the bar. Is this the correct sway bar for this car? Who knows? My car is not a factory sway bar car. I bought this sway bar in 1989 from a guy who had an ad listed on the back page of the Plymouth Barracuda/Cuda Owners Club newsletter. He said it was off of a 65 Barracuda, but I have no way of knowing if he was telling the truth. It could have come off of a Citroen for all I know. He shipped it COD; remember those days?
Anyway this sway bar does have the weird looking "squished-squarish" sway bar bushing mounts . I ordered the GG80C bushings and slid them easily onto the bar. I tried every method and technique to get the bushings pressed into those "squishy-squarish" brackets. I used soap, silicone, press ,sacrificing a live chicken... you name it. All those efforts got me was a split and broken bushing. So I had to order another one.
So I cut the bracket at the weld, pried it open a little, slid the bushing in, clamped it back together and welded it back. I was worried about overheating the bushing because a) it's a rubber bushing in a piece of hot metal and b) I am NOT a good welder at all. But everything turned out ok. Seriously, nothing smoked or distorted. Not gonna lie, these bushings don't exactly fit perfect (remember we are taking a square bushing and putting it in a "squarish" hole) but they do in fact work. My old bushings were so worn out that pieces fell out when I removed the bar so I can't even compare the shapes.
Anyway, a quick paint and some new end links and it handles as well as it ever did back in the early 90s before everything wore out.