Mancini extra heavy duty springs sagging

Sorry,I re-read your first post,and you stated the drivers side is low. That is the way the springs are designed. You have them installed the Correct way.

If you want the car to sit level,there are a couple ways to go.
You can buy another drivers side spring and install it on the passenger side. But with the
unknown history of these springs,getting the correct spring could be a crap shoot.

Or sell this set as Super Stock springs,and buy a new set of stock replacement springs.

Re-arching would be a waste of time/money IMO.

There are people on this site that will buy your SS springs.

PS: Can you show us some pics of the car ?