ZardozCongrats on beating Mission 34. You aren't going to get a lot of responses to this request because very few of us have the R89C. This is, in fact, the first tuning request I've seen for that car.
All I can say is that using a lot of TCS, putting harder tires on the rear, and using a brake balance of 4/1 is a good start. You might do a search for R92CP settings because what works on that car should work on its older sister.