Springs for 1968 rear end transplanted into a 1966 Catalina
 

I have a 1966 Catalina with a donor 3.42 posi that I was told came from a 1968 full size. It's been under the car and operating for many years and it never bothered me that the 66 spring bottoms are much larger than the round anchors on the 68 spring perches. But now it does bother me, so does anyone know if I can use 68 full size springs for this setup? Will springs for a 68 have the appropriate spring rate and height? Will the top of the spring fit the 1966 body? Thanks for any information anyone may have.

If you are content with the current ride height, make some centering rings to match the spring inner diameter and perch outer diameter. I think 68 springs have the small diameter pigtail on both ends(?), which wont work well on 66 large pigtail frame.

Arowhed, you're right. I called Eaton and asked them about springs for a 66 vs a 68. 66 springs have the same size larger pigtail top and bottom, while 68 springs are small on both ends. So yes, some form of adaptation is required. The good thing is that I have springs that CAN be used. 68 springs couldn't be used with a 66 chassis at all.