I decided to looks at my rear shocks today. The left shock had no resistance to movement but the right shock did. I have the truck box off for rebuild, and the shock bushings were all but gone. I had removed the knurled pin awhile ago so they were free to move by hand. I unbolted them from the frame and took the left one into my vice and removed the fill/check valve plug. The manual does not give much info as to what type oil to use so I decided to use ATF. After filling and working the lever to get the air out, I put the check valve back in and reinstalled the fill plug. The left shock seems to work just fine, lots of resistance going down and not much to return coming back up. So I did the same to the right shock after draining the remainder of oil out of that one. It works nice too, just like the left one. Is there any reason to not use them? Do most people upgrade to the modern shocks? These, if working should be fine in my opinion, and other than new rubber bushings and pins, did not cost a lot to repair.

1947 3600 Chevy