Do you mean to 3" to scale?
The mod I did only alters the cars suspension by a centimeter(100mm) or less
"With a rally car, you're putting the driveshafts and suspension at extreme angles, which may well cause the driveshafts to pop out."
I only altered the rear suspension, which sits lower than the front to begin with, now the rear driveshafts only extend / bend about as far as the front ones do, and since they use the same axles/cups it shouldn't be a problem.
As for bottoming out, ideally the suspension would essentially end at the point where the wheels are levels with the frame, allthough unless you are doing huge jumps the suspension should be able to handle it. As for shock, I'd rather have it go through the shocks than through my servos/motor/ etc located in the body.
I drove it today and it handles almost identically as it did before(since the rate of the suspension remains the same and CG is only altered slightly , this is not suprising) including amount of tail "hang" and drift. I also pulled the small c-clamps off the rear to level it off a litlle. I'll post pics as soon as I find a way to get my Sony digicam to work with my Mac.