tighten up

I great starting place is to yank the sway bars from a V8 mustang. They got a solid front bar (as compared to the hollow 6cyl bar), and there is a rear sway bar (as comparted to nothing in the v6). These will really help take out the body roll. Both are very easy to install, and you should be able to locate them for less than 100 combined.
I don't see a great need for subframes, since you are already starting with the more rigid SN95 chassis.
If you still arn't satified, try some stiffer springs and struts.... but then you will be in the same place as me... snap oversteer city and wishing you could afford a panhard bar!