Here is the original diff out of my Holden (upgraded to a 9", etc) and can see they just use a normal round bushing, same idea as a Chevelle basically but with longer lower arms.

I used Aussie made poly bushing in it, but of course there are all durometers out there, these comply enough but no sloppy feeling. No issues with binding excessively from too stiff a bushing either that I can tell. Only different style bush in all the 4 arms are the uppers which I bought from here in adjustable to dial in the pinion angle. (The ones in the diff housing the upper arms mount too are the same Aussie ones in the lower arms)