For me a gr. C car from Legendary detuned.
Maybe the Porsche 962C or the Mazda 787B.
Detuned you don't need to save fuel at all, it's the tires that define your strategy, because of the rain.
You can keep the fuel map on one and do 4 or 5 laps, fuel related, depending on the tune and how much you have to slow down because of the rain. As said, the rain usually appears always at the same moment, by the end of lap 2, but the intensity is variable. Sometimes you can keep going with slicks, sometimes Inters will not be enough for the water on track.
The hard part is to decide to put Inters/Wets on end of lap 2 or not. I suggest putting weather radar on less zoom possible on the MFD and decide by that and not by the current level of water on track.
If the rain is short you don't need to stop for tires and only stop once for fuel when needed and don't even need to top the tank, the RH are good for all race, no need to change.
With rain I had times where putting Inters at end of lap 2 was too soon and others that waiting for lap 3 was a disaster, on first tries, where I relied on visual impressions and the moister meter instead of the radar.
When stopping for Inters or Wets, I use to top for fuel, just in case I don't need to stop again, If I need to put slicks again, specially the wets just melt on drying tarmac, don't need more fuel, just put the tires.
Just be aware that detuning too much power could make the car stall on 3rd gear for top speed, with too much drag for the power output, specially with stock gearbox, as they have extremely long gears to save engines and fuel at the long straights with much more power, specially the 80's group C, when Le Mans didn't even had chicanes. Once I was too radical on the Porsche, because I didn't want to put ballast and the car just stall at 150 mph on 3rd gear.