Take the magnets out, you don't need them, especially for a rally car.
The MRRC 911 has an accurate body for an early 911, but the chassis needs a little work to make it handle and the motor is over geared.
The Ninco 911 is also to scale and it's chassis could be used with either an MRRC body or an ARII one, it definitely fits the Arii body.
I think the Scalextric and SCX 911s are over scale, but haven't checked.
The Fly Racing 911 is also good, the ordinary Fly 911s look nice but the motor positioning makes the handling interesting.