This is one of the photos that secretly drew me into sport. It was in a book called Grip strength, which is sadly no longer in print. I think it is of a man called Joe Falzon who is now 80 and still fit. Joe Falzon was a great strongman on the island.
Perhaps you should warm up before doing this exercise, a little light jogging, or skipping might be in order. Repetitions and sets, are left to the trainees judgement. The wearing of a Beanie is only really appropriate if you are a "Boulderer", or are thee "Joe".
There are reportedly 6 people in the car so, and I swear to god the guy leaning on the car looks like my uncle.
Good luck with this exercise, remember progression could mean more guys in the car, or more uncles leaning on it!