An FF01 chassis as a rally car would be pretty tough. You might try finding a cheap TA02 chassis w/ the shaft drive to use as an offroad rig.
I have an FF01 (Tamiya VW Golf VR6) and its great for street.
You'll likely be limited on the amount of droop in the arms. The FF chassis doesn't give that much and to truely make it rally worthy, would defeat the purpose OR require too much modification. not to mention grass would kill it.
I would look at something like this:
Great little rigs, fairly inexpensive and you might even find one used.
HPI still makes rally tires and wheel which should fit. Older HPI RS4 arms could be adapted to give the car a wider stance.
(unfortunately the Rally craze was a few years ago and the HPI RS4 Rally and TC3 Rally conversion were hot tickets. Now both are disc.)