OK, here is my $0.02 worth. You have had a lot of good advice so far. Some of it is probably a little more race/performance oriented than you wanted. I understand you won't be racing, but want a good handling car in 'aggressive' traffic. Here are my thoughts on a well handling almost daily driver car that should perform well without breaking the bank.
1. Front end: First let me say that although you might not have much luck on the Autocross circuit with a stock, 50 year old Mopar suspension, there is nothing wrong with it for what you are talking about. You do not really need tubular control arms to achieve a good handling car. Contact PST for a poly-urethane front end rebuild kit. They are a sponsor on FABO, they give us a 10% discount and their stuff is good quality. You could look into boxing in your LCAs. I have heard that this will improve handling, and if you can weld the cost would be minimal. While the front end is apart for the rebuild, paint all parts (like UCAs, LCAs, etc.) with a decent quality paint. Eastwood makes a spray bomb chassis paint that is very good, and will hold up much better than Krylon or Rustoleum. Have the parts all sand blasted before painting. The front sway bar will make a big difference. It might not be a bad idea to get new torsion Bars while the front end is apart.
2. Rear end: Don't throw any money at your current rear end. You said you were going to replace it with an 8.75 next year. So for right now I would just do a good brake job on the rear and call it good. If your springs are weak, a new set of rear springs would be a good idea. Get them now ONLY if they will be a direct transfer from the 7.25 over to the 8.75.
3. Tires: Although I agree that for maximum performance you might want to switch to 17 inch rims and tires, you said you were not going to be racing. So I see no reason to dump several thousand dollars here. Cooper Cobras or BF Goodrich Radial TAs would be a good selection, but there are eof other decent 15" tires. Look at
www.tirerack.com. Any decent quality, modern radial tire will give you what you want. If you want raised white letter tires, I will warn you the the white letters on the Radial TAs tend to yellow and become no longer white prematurely.
4. Brakes: I had 10" drum brakes on my 69 Barracuda Fastback. about 10 or 12 years ago, I did a manual front disk conversion and WOW what a difference. I do not regret not going with the power brake kit. Manual disks on the front with drums on the back work great. You should be able to do a front disk conversion and a rear brake job for about $1000 or less depending on what you select.
I am guessing you can do all this for around $2500 to $3000. Now I know that some guys are going to poo-poo these suggestions, but if you are truly focused on a non-race car, you can achieve the level of handling and braking you are talking about for WELL under $5000.
