Won't hold alignment?! Something is seriously wrong there - not just worn bushes...
I've used SuperPro purple polyurethane - harder than rubber, but not as harsh as the red Nolathane.
Very easy to install, but it depends on your skill level.
If it has the original damper inserts in it, get these re-oiled - much better option than installing crappy Monroe etc inserts
Kings lowered springs are excellent for doing the highway duties - firm, but supple enough to take out road vibrations.