Start with what the McLaren 650S GT3 is: a car with gasoline engine, from Mclaren. What it meant takes a little longer.
The engineering
The engine is gasoline engine. These are manufacturer figures carried by Wikipedia and Wikidata, not road-test measurements.
Where it sits
Its Mclaren stablemates include the McLaren M15 and the McLaren M16.
The record
The open record for the McLaren 650S GT3 carries no verified engine, output, weight or price yet. MotorJury does not fill gaps with guesses; this entry gives the model a home in the catalogue and grows as sourced specifications and photographs arrive. Corrections: corrections@motorjury.com.