One other option that I plan to use on one of my cars (daughter's car) is to get an old set of 65/66 Mustang rear springs, remove the top spring and cut the eyes off (cut to length). I have a friend who has a few extra Mustang springs laying around and he gave me a set. I cut the ends off (eyes) leaving a very long top spring. Then, once you have the Mustang spring the correct length (to support the Mopar top spring) you remove your old springs, disassemble, reassemble with the Mustang spring, drill a new hole in the Mustang spring for the spring bolt and reinstall. This should do two things: it will raise the rear about 3/4" to 1" and also take some of the "sag" out of your old spring.
Here are some pics of the two Mustang top spring (with eye removed) next to a stock 67/68/69 A body rear spring. On the A body spring the second leaf is quite a bit shorter than the top leaf. The Mustang leaf is almost a long as the Mopar top leaf which should enhance the arch and raise the car.
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That's my plan on how to spend nothing and get something!!
Treblig