What size front T-bars are you running?
The SS rear spring are sort stiff. Adding a rear sway bar might make the car real oversteering (loose/rear hanging out). This is were the helwig adjustable rear sway bars would help dial in the car.
If you were going to bother with race autocross compound tires I would pony up to something 255 or 275 wide in front and rear. You want both the same and same rims so you can rotate the tires. Will need a wheel spacer for that.
IMHO, I would fit 275/40/17 tires on 17x9 rims. Thats a fairly common size or tire and rim. Might need to trim the front bottom fender lip.