Don't waste money on a t/b for your set up.

I would say diff gears (not bigger than 3.7's seeing as your thinking of maybe going to manual later) as this will make the biggest difference out of anything to your car.

Secondly headers. Pacemaker comps are good, but the normal version is fine too. Any headers with mandrel bent pipes will provide similar results to each other, with semi-tuned length versions (ie pacemaker 4480's) providing a little better. My advice would be to look around second hand as you can get some good bargains on headers.

For a cat converter you shouldn't be looking more than $150 for a metallic one.

As for a cam, I would recommend a wade 1636 or a 1673 if you get shorter diff gears done. I'm not sure on JMM cams but other members will be able to tell you what will work with an auto.