Definetly don't need to dump almost 2 mil on the 97 Supra GT500, just for this race, specially since the top speed isn't the strongest suit for the old Supra. I believe most of the people who use it, that's because it was a bonus car for those of uss who bought the game in pre-sale, so it was a go to car through the menus and so for us.
For very confortable wins there are cheapest and fastest ways.
Just be aware that a road car tuned may no be your cup of tea and could get expensive aswell. Engine swaps are a rare comodity, specially to those who didn't had access to the multiple reward from the same menu, some updates ago.
Don't really need a car than can do the all race without refuelling, most of the timesyou will have to stop for tires, but it's nice if a car can do, let's say, 4 laps on fuel, because gives you flexibility on the moment to stop for tires, depending on the rain.
That said:
The budget option - Alpine A220 (Legend Car Dealership) - for about 330k, it overpowers everything at 700pp, and goes forever on fuel and tires too. But a bit dodgy handling, not for everyone and you still have some tuning to spend money (turbo, intercooler and gearbox). But all around still cheaper than heavilly tune some street car.
The easy win, not extremelly overpowering option - Aston Martin DB9 GT1 (Brand Central) - It's a gr. 3, like the Supra, but much better suited to Le Mans, has good top speed and fuel efficiency, it's very neutral on handling too. It's available on Brand Central so not depending on any rotation/slot availability, but is slightly more expensive than regular gr. 3 cars, at 800k, still less than half the cost of the Supra.
The sensible money dump: Aston Martin DP-100 VGT (Brand Central) - This is a bigger investiment, a whole million but this is the car that literally pays itself. It has amazing fuel mileage, it's extremelly kind on rubbers, has four wheel drive, so no problems on wet and even has the street car hashtag, so can be used on events restricted to road cars. Just need to fit on it a medium RPM turbo. Overpowering at Le Mans on 700pp form, it's an easy win, not stop at 600pp with sports hard at Tokyo WTC600 and also at the Human Comedy mission 1 hour at Deep Forest. The only downside is that needs to be massively shortshifted, as it has no power on top end and to save fuel, so not so strong with people using automatic transmission.
Just plain overpowering: the old Gr. C car of your choice (Legend Car Dealership) - Slightly bigger investiment than the Supra (well, the Porsche 962C could actually be bought for less money than the Supra) but this cars can do 6-7 laps on fuel, so just stop for the right tires. Any of them will win you easily Sardegna 800pp race and are the best cars to Neoclassical Challenge too.
To be honest, used a lot the 97 Supra GT500 at the beginning, as it was a bonus free car, but since my garage had alternatives, no much use of the Supra GT500 really.