Fair enough. You'll want to setup closer to ralley setup than road course or even autocross. Autocross assumes relatively smooth surface, and gets some heat into the tires - also most competitors want a 'loose' setup which is not a good idea for real street use.
It helps to know what your car weighs and how much is on the rear springs. Then you can get the height you want using rear spring rate and free arch. Options include:
a. Rick E-berger & Co. along with others have had good success in dearching SS springs for road course/street. Look up the Green Brick, especially the low buck approach they took the first time they were successful (not the first time).
b. Made in the USA replacements for A-Bodies based on factory specs from Stanley Spring. You may be able to buy locally. Here's a retailer that will ship http://www.stengelbros.net/Plymouth-Leaf-Springs_c_226.html Notice that Plymouth and Dodge had different leaf packages depending on the car's configuration.
c. A company like Firmfeel or Hotchkiss with strong interest and experience with rwd mopar handling who have developed options that generally work for people like you.
Probably a good move. 340 bars are OK with soft rear, but even on rougher roads, with todays tires, you'll probably be happier with a t-bar as stiff as 200 #/in or so.
Actually, a front sway bar is the most effective thing you can do. I'd start with that.
Do not add a rear bar unless you've added front anti-sway bar and preferably also increased the torsion bars. Do not add a rear sway bar if the rear is already very stiff. When the rear's rear roll resistance is too stiff relative to the front, it will have a tendency to fishtail rather than plow. This will happen when traction is lost, which of course is the worst possible time to find out.
Basically yes. Good shocks are worthwhile, but not cheap. Front sway bar is a great bang for buck. Lowering the center of gravity and roll centers is good. Depending on your roads, 15" tires will be OK. If they're real bad, then maybe look at 15" rally tires, which provide pretty good grip over a wide range of junk, not cheap. Otherwise I think people have already provided good advice from their own personal experience. I actually run 70 series 14s on the street, 15s only for competition, but selection in 14s is worse than 15s.