As mentioned, the generic name (which was also the Monroe trade name) was "Load Leveler" shocks. If you look, the coils in the middle are closer together than at the ends. This results in not a lot of spring tension in the normal "ride range", but added stiffness when there is additional weight in the back.
When I got my '70 DH43N car, it had them on the back, as did my '67 Newport CE23. The '70 had been used to pull a travel trailer with, so the rear springs were tired, but the rear end of the car sat lower anyway. So, the answer to the question is "No, not designed to raise the rear ride height, just keep it more normal with a load."
I bought the car in '75, so no spring shops were known to me at that time and Chrysler had discontinued the OEM parts springs, so the best option I had to raise the rear end was
Gabriel Hi-Jacker air shocks. They have served me well, although others in here hate them. BUT all I did was raise the rear end enough to level things up! NOT elevate the rear end to clear some L60-15 tires for "stance of the times". Not being in a state where road salt was used in the winter, no issues in that respect, either (as to the crossmember where the upper shock mounts are).
ONE advantage to the air shocks is that their core is a larger piston bore diameter, as HD shocks had back then, so a more controlled ride. The LL shocks have the base 1" piston diameter, so nothing HD in that respect.
I was not aware of any adjustability, as to spring pre-load on the LL shocks. Never did worry about it, though. Is that something new?
To determine IF the rear springs have "sagged", FIRST get the front suspension adjusted to the specs in the factory service manual. You'll need a BIG socket, socked extension, and break-over bar for best results. Seems like the distance between the lower control arm bumper and its contact point was basically my index and two adjacent fingers wide? Or nearly that wide.
Then, park the car on a level surface and look at it from the side. If you take the gap between the rocker panel and lower door, then extend it forward and rearward, notice where it crosses the wheel cover. It should cross the front and rear wheel covers in the SAME PLACE on the covers. If it is lower on the rear covers, the rear springs are weak from age/use. That "line" should be parallel with the flat road surface at factory wide height.
When you look at the factory distance specs in the FSM, the dimension for the larger spec is for the factory HD suspension, which has more leaves in the rear springs. So that additional height (at the rear end) results in the larger distance spec for the front suspension. To keep the rocker panel parallel and at the correct ride height.
Just my experiences and observations,
CBODY67
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