When I replaced the cab bushings on my '75 I realized that the old ones had collapsed so far that the cab was sitting on top of the transfer case. Really reduced the cab noise when I got rid of that metal-on-metal contact with the cab floor. It also pulled my shift linkage into place so that I could start the truck in both neutral or drive, which had never worked before. IIRC, the radiator support bushings were part of the complete cab bushing set.
I replaced the cab bushings with the truck parked in the driveway, and used a short section of 2x4 to push up and hold the cab while I removed and replaced each bushing. I was luck and could break each bolt loose with a fairly short breaker bar. I used poly bushings and lubricated them, but they still squeaked on and off for a while. They finally settled into place and got quieter.
Bruce