I always tune my cars primarily for handling, so losing the R3s provided a nice and welcome challenge which i've adjusted all my 600PP cars to without much trouble. Suspension is the key here, your car will never handle like it did on R3s with S2s, but it's not that difficult to create a controllable and fast car to go with online.
Good starting point for an RWD easy to use car is the Amuse/Opera 350Z, but i've got a Tii, F430, 512BB and of course my old Evo IX/Tuned all running in the top 3 each race (if i can keep the 512 out the sand!).
Camber and toe helped me most but i won't say anymore. If you really can't manage it, grab an AWD like an Evo X (not tuned).