Roger, welcome to the board!
Sounds like you a have good plan to make your car handle. What you are planning for the rear suspension mods? Do you have a tire size in mind? With 18" wheels you have a lot of options for tires. The BFG
Rival in a 245/40/18 would be a great choice.
I ran the following on my
Chevelle and enjoyed some GG autocross & ASCS events. I would've liked a bit more sidewall in the rear because the contact patch did not change when I aired down the tires.
18"x7" - 225/45/R18
20"x8.5" - 245/35/R20