Springs for 1968 rear end transplanted into a 1966 Catalina
 

I've also asked this in the "61-66 Big Car" section but maybe there's someone here that knows. Many years ago I put a big car posi rear under my 66 Catalina. I was told the housing was from a 1968. I'm riding on 66 Full Size springs and I've just ignored that the bottom of the spring is much larger than the circular perch. Now I'm wondering if I should use 1968 springs to match the bottom spring perches. Does anyone know if 1968 Full Size springs will have the appropriate spring rate, ride height, and top diameter to work in a 1966 Catalina?

Just swap the perches. You can call Eaton spring and they can answer your question, but the 68 springs may have a pig tail on the top and bottom

stevep, I did call Eaton. That was a great idea. Their tech adviser looked up the different spring dimensions and told me that 66 springs are about 3 3/4" on both ends while 68 springs are 2 1/2" on both ends. So you're right, the only solution is to adapt the 68 rear end to fit the 66 springs.

We put a 66 3.42 posi rear in a 68 about 20 years ago and just changed the perches