Hey RX7, how new are you to the game? I'm assuming you're pretty new to gt2. Also, what version of GT2 do you have? version 1.0 has a lot of weird bugs and bad programming (car wash says it costs $5,000 but really charges $50...Taurus turns into Mark Martin's NASCAR with racing mod). If you have version 1.0, sometimes a Vector will appear in the lineup and you wont' be able to pass it from what i've read.
If you have version 1.1 or 1.2 (greatest hits) don't worry...295 horsepower is overkill, even for a amateur racer. I've won the TM enduro many times...most recently i conquered the race up against the mighty Lotus Elise 190 in a 150 hpish Subaru PLeo RS! I used the car's stock tires and a semi-racing suspension...it took me quite a few laps to catch up with the Lotus, but i won. If you're not familiar, the Lotus will be the toughest opponent since it's so light, but more than half the time it doesn't show up in the race.
Like i said, even if you are a bit green, you should still be able to win this race. I forget how much power an RS has...i'm guessing somewhere between 220 and 276 hp. You might wanna add a sports suspension to those sports tires, and maybe get a sports transmission, too. This is all you'll need, RX7. Full custom suspension is overkill, and i hate to tell you, but going into detail with suspension and transmission tuning won't make much difference here, you'll win even with sloppy driving because RX7's generally handle extremely well with such low power. I wouldn't bother with limited slip, either.