So,

I have done some searching on benzworld.org and here, I posted the same thread on bw.org, but only had one response.

So here is the deal:
I bought a cheap 1985 300td from a young guy in Philly, it was a mess. He said the PO had removed the sls. By that he meant that the guy had put 300d shocks in the rear (blown), and removed the pump from the engine. He left everything else in tact.

I needed to get it on the road, so I put a pair of Bilstein HD shocks for a 300d in the rear. The car is still bouncy, as I know the sls shocks were supposed to take some of the load.

I have been searching, and saw hints of putting sd springs in the rear can help. I also was linked to these springs:
http://www.slsconversion.com/

I have access to many mercedes in the salvage yards around Baltimore. Currently there is a 1982 300td in a yard, and I was planning on getting the pump, actuators, and shocks.

I lack experience and time to put the sls back in right now, but I am looking to do something about the rear springs. Is there another model benz springs that will help my bouncy/sagging rear end (no pun intended)?

best is of course to get the SLS back functional. if you have access to the parts, there are DIY writeups here about doing the install and the adjustment, even the rebuild of components.
many have suggested that SD springs would improve the ride with HD shocks, but that would be with NOTHING in the rear of the wagon, and I'm pretty sure, they mean NEW SD springs. not used saggy ones.
there are threads on here discussing this very subject, do a search with the upper search link, and choose the google search portion, and use keywords like SLS swap to SD springs or similar.

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John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Couple ppl have had sucess with the conversions on superturbodiesel.com. Some searching and you will find what you are looking for. S600 springs or "progskin".

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http://superturbodiesel.com/images/sig.04.10.jpg
1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

i've got a set of the propigskin SLS delete springs that i'm selling - bought them but then sold my wagon before they got installed.

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'81 240D 4 speed
'97 E420