Unfortunately, the 4 MX-5's names change region-to-region, and I'm not exactly sure which is which.
One of the two 1998 shapes (non-poppy-up headlights) has 168hp after you oil it. In PAL this is the 1.8RS. This is the car you want to use.
Slap on T3 front tyres and T4 rear tyres. You'll need to pit roughly every 10 laps (3 stops) and you should be finished in about 1 hour, 8 minutes. The lead car is ALWAYS on T7s and pits every 3 laps, so don't worry about him - he'll finish last.