There are a number of things to do to help the handling; Alignment can make a big difference- Get as much POSITIVE Caster as possible, then get some new (After-market) upper ball joints that allow Negative camber (Wheels in at the top).
Most of us like big dang wheels and tires on our cars- but resist the temptation to go too far in that direction because heavy wheels and tires KILL the feel of the car (And performance) Look at a C7 Grand Sport Corvette- It has 285 mm wide tires up front and 335 in the rear, but the car weighs approx' 3500 lbs. A Fiero weighs around 2700 lbs so that gives a ratio of 1.3 to 1....So the 285s become 220 and the 335s become 255......I actually went with some 16 x7 wheels that are very light (14 lbs) and some General G-Max All-season tires sizes 205/55 and 225/55....The Generals have the added benefit of being somewhat lighter than other tires (Especially BFGs)
I have also switched the rear subframe/suspension to 88 on my '85 SE V6 which really makes the car drive/ride/handle better.
And finally, I came up with a way of mounting the stabilizer bars which makes them vary their strength during acceleration and braking, helping both turn-in and drop-throttle over-steer....Here is a link to my thread on this idea; http://www.fiero.nl/forum/Forum2/HTML/140674.html