For a street car stick with the stock K member like swinger said. If its off the car now, do a reinforcement on it by seam welding everything and gusseting the steering box mount.
Install a bigger set of torsion bars. 1" at least, up to about 1.06" unless you're planning on tracking it. The torsion bars alone will make a HUGE difference, especially with subframe connectors already in.
Sway bars are a great addition. You don't have to get the biggest ones out there, especially if you've gone with bigger torsion bars. An adjustable rear bar is a good idea, as these cars don't usually need as much rear bar as they do front. The rear springs are pretty close to the right spring rate, so unless they're totally worn out you can actually use the stock rear springs for a while. Of course, if they're sagging like most are they should be replaced.
Shocks are the next big item, a good set of shocks like the RCD Bilstiens or Hotchkis Fox's are a huge addition. Depending on what brakes you already have, you may be able to leave those alone for awhile. The stock disks work fine for the street, and you can upgrade to 11.75" disks with just a set of caliper brackets if you already have 73+ spindles. Those work pretty darn well, you can hold off on the super expensive big brake kits if you go that route. I run 11.75" mopar rotors and the stock calipers on my Challenger with 11" rear drums, and it stops very well for a big old E-body.
Tires are a HUGE improvement as well, go 17's or 18's with a modern compound tire. Set up correctly, a Demon can run 275/40/17's all the way around. Or 255's if you don't want to get that crazy. That by itself will do amazing things for your traction, which is why the bigger torsion bars are so important. There are pretty much NO performance street tires in 15" anymore, BFG T/A's and their clones are barely a step above hockey puck rubber.
Of course I just laid out a few thousand dollars worth of parts, but I'll add some good news. You don't need tubular ANYTHING. Not UCA's, not LCA's, not the K member, none of it for a street car. I'd also stay away from heim joints on the street. Get a set of offset Moog UCA bushings and a set of stock BBP UCA's and you'll be fine. If you really want to, tubular UCA's would be my exception to the tubular rule because of the built in adjustment for better caster, but make sure they're the bushed kind for the street. You'll be much happier. I've run tubular UCA's and LCA's for around 40k miles, and still have a set of Hotchkis UCA's with heims and the difference vs. rebuilt stock parts with poly bushings is almost non-existent on the street. For a track car it will make a difference, but for a street car its mostly just a headache. The adjustable heim UCA's take some setup to get right, so unless you're doing your own alignments there's a few trips to the alignment shop. And the heims wear quicker than poly or even rubber bushings on the street. And they're expensive, and that money is better spent elsewhere.