I looked in a Batco catalog from about 40 years ago and there is no listing. Batco, which went broke in the 1990's was the best source for odd stuff. In my previous post, I didn't mean to remove them all together. But they really don't do a whole lot other than keep the axle in place which doesn't require much. Spring ride trailer suspensions still use a similar set up except for not having any shackles at all. I think GMC only used this setup a few years. I think that you will probably have will have to get the nearest thing you can find to fit. Fitment is not all that critical. I just don't take mine apart because if I do, I will have to find something to keep them from rattling around. And I would have a better chance in finding something to fit because I still have a lot of parts for trucks and trailers that I junked over 30 years ago.
