IMVHO your GTS looks perfect as it is (40-series rear tires and original wheels). There are a plenty of hot rodded GTS´s but very few as clean and mean original looking ones as you have. But then again, who am I to preach any one about this issue, considering what my car will go thru´.
Really looking forward how your car is going to feel like when it´s finished. Then I can hire you for an unreasonable fee, as my personal transmission conversion consultant...

I´ll post an update about mine in a while.