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No single word more important when it comes to the design of a sports car! Porsche has been building and competing rear-engined sports cars for over 60 years. Whatever sort of tweaking one could imagine has already been tried by now.
With some research, you can find out whether your ideas will work before even attempting them. According to their website, Porsche has 20,000 different racing parts for sale. The car owner can call Zuffenhausen and tell them what he wished to do with the car, and they will tell you which part(s) to use, and where on the car they should go. They'll even build the whole car for you from the ground up, based on your intentions.