There were a couple of style mounts that Chevy used the regular style and then they had these
This style gave a much smoother ride but were prone to sagging. They seem to be used on 3/4 ton and larger trucks perhaps to help counter act the stiff ride due to the heavier suspension. I had them on my 63 K20 and they were nice but started to seperate after I started to put some miles on the truck. I replaced them with the brackets and new Polyurethane bushings from a 63 GMC C15.