I'm going to pretty much agree with what's been said so far. Replace all of your bushings, ball joints, tie rod ends, etc. You can go either with rubber or polyurethane bushings, the polyurethane will firm things up and give a more precise feel, but they also tend to squeak. A lot. So you may want to stick with rubber if you're going to be driving it a ton.
I would go with 1" torsion bars, I think that on an A-body they should be about right as far as spring rates for compromising handling and comfort. Any bigger will likely be pretty stiff, especially if you go to shorter sidewalls with a set of 17" rims.
Front and rear sway bars. You may not need the rear depending on your spring choice though, if you go with SS springs they're rate is about 160 lbs, which is more than stiff enough without a sway bar. XHD's could still use a rear bar.
New rear springs. XHD's are decent enough, you can go EXPO if you want a custom arch.
New shocks. If you're building a serious corner carver or racer the Billstein's are awesome, but if you just want a street car that doesn't wallow all over the place a set of KYB gas adjusts will be fine.
If you do all that you'll be able to tell right away if your steering box is any good when you get back on the road, any slop or play left will be the steering box. Firm feel does awesome rebuilds.
The alignment specs above I don't agree with. Positive camber and modern tires are not a combination for good street manners. This is the set up I run on my Challenger...
-.7 degrees camber
+4 degrees caster
1/16" toe in
For a regular street car -.25 to -.5 degrees camber is fine, I had mine set more negative because I'm trying to set the car up as a serious corner carver, and I just like the way it handles with that amount of negative camber. I also have tubular a-arms with a bigger adjustment range, you may need an offset bushing kit to get those numbers. Anything more than -1 degree camber will wear out tires on the street, too much straight line driving. +4 degrees caster isn't necessary either, you may not be able to get that much even with an offset bushing kit. Its good for power steering, especially the mopar "no road feel at all" power steering. But that much can make the steering a little heavy if you've got manual steering.
For an example on negative camber, check out the tires on this 'cuda set up for Pikes Peak. Negative camber=better cornering. I would suspect that to be between -2 and -3 degrees.
Not my picture obviously, credit to Mike Rogers. I believe I got it off of Flikr.
