Fix the oil cooler lines asap. As said above they could do a lot of damage.

Now is the rear sitting low? Bistein comfort shocks can be had for around $70 each. I don't think HD's will do anything except give you a stiffer ride. I would try to find out what is causing the rear to sag. The rear sway bar isn't a big deal snag one from a junker and if you want paint it and throw on a new set of links and bushings, figure $50 painted with new stuff.

If the rear is sitting low check:
1. rear springs
2. diff mount
3. subframe bushings.

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2006 CL500
1969 280SE
2023 Ram 1500
2026 Genesis GV70
2007 Tiara 3200