You can't win that one fairly. I can manage to get 1st about 50% of the time and 3rd the other 50%. You HAVE to do it in standard (unless you have God-like driving skills). Also, you need to cut corners. Here's my guide:
Setup:
Standard physics (I know it's noob but it's the only way)
TCS 5 (that way you can floor the gas and execute passes quickly - executing passes quickly and efficiently is crucial)
Forget how you normally play GT, this one requires you to cut corners and use other cars as brakes
ASM - your choice, i leave it off
ABS - 1 (unless you're really good, otherwise leave it on 1 and just slam on the brakes, guarantees quick passes)
1. Overtake the 599 and DB9 in front of you at the first corner (a must, if you don't manage to get the DB9 it might get tough)
2. Try to overtake F40 at 2nd corner (the right hander hairpin)(Easily done cleanly if you've manage to pass DB9 quickly, if not, ram it)
3. Slipstream and try to take the TVR at the turn where it's a little bend to the left
*If you haven't passed both the TVR and F40 by this stage chances are you won't even get 3rd*
4. Try to overtake the 2 closest cars to you (ISF and something else I believe) (doesn't matter if you don't manage to overtake both, you can easily pass them at the next corner).
5. Get as much slipstream as possible and overtake as many cars as you can at this next left handed hairpin. If you can manage to pass the Corvette or come out of the hairpin right behind him then it's looking good so far
6. Slipstream as much as possible and pass this pack of cars, up ahead should be another pack of about 3-4 cars. Try to get as close to them as possible before the next turn
7. *IMPORTANT* DO NOT TAKE THIS TURN CLEANLY. Try to pass all 3, or at least 2 of the cars of this pack by cutting the track. Brake very very late and do not bother using the road. (I take this turn in about mid 4th gear or high 3rd gear) Cut across the grass and get back onto the road as quickly and smoothly as possible, get a bump from anyone or don't do it smoothly enough and you're going to restart.
8. You should now see an F430 and R8 in front of you, these two cars are the leaders of the race and to win you must beat them. If so far you have managed to passed the cars where I have said you should pass them you should be close enough to pass them by the end of the race.
9. Take the next chicane as quickly as you can (you can do it cleanly or by cutting it, I don't see too much of a difference)
10. Try to get into their slipstream and hopefully pass them! (You can try taking a shortcut through pitlane but so far it's never worked for me)
By following that you should be able to get 3rd and 1st pretty regularly with some practice to locate the best lines and figuring out the lines of the AI.
Note: I am not a cheater in GT. I love playing it realisitcally (Pro physics, no aids, no ABS, clean driving) and generally do not resort to cheating. However, I cheat in this event because it is impossible to do otherwise, and it is one of the best ways to earn money in A class.