Have you checked out Kirban's? I run the variable rate rear springs and have been very happy with them. Back seat passengers and full trunk no problem.
ROCKAUTO.COM is probably one of the cheapest sites to get the moog springs from. With a 5% discount code 712290255106 is valid, you can get the Moog 5662 and the CC627 cargo coils delivered for about $130.
Those G-body cargo springs are all you need. Pretty inexpensive and will hold your wheel lip about 3" above the tire. It's been a common replacement for all G-bodies for over 20 years. You don't know how may I've seen in my junkyard excursions. They were a dime a dozen. My Dark red T, pix below, have them on it.
Would you go with the Moog CC627 for the rear or the Moog 6321's? I do not want a lifted rear end, I want the rear to be at factory ride height or slightly lower.