[Entropy11]

From everything I dug up, the 5399 was a direct replacement for 2nd gen El Camino. I believe the GM part number for that original spring and the later year wagons were shared for one of the years at least. Actual (listed) spring dimensions for the 2 checked out. I use the SMS5399 to add about 1-1.5” rear lift to A-body cars I’ve had.

My apologies for not seeing you call out your Catalina specifically, I must have skimmed over that part and lumped the question into the standard “raise my a-body rear” question that pops up.

I do know that as far as a-body springs are concerned, the HD springs contribute zero to ride height change and just equate to rate/stiffness change. I can grab any measurements off my springs here if it’ll help at all.