I am wondering if you mean distributed or organized. I can not think of anything in A Separate Peace that dated the prizes. The only date I can think of is the fact that they held the Winter Carnival on a Saturday. They also did so secretly.
It was not really an organized event in terms of the events, it started with a mad dash of all the boys attempting to get the hard apple cider from Brinker. From that point on out, it was chaotic, and the games ended with a ceremony celebrating Gene's accomplishment (which wasn't much) to mirror the Olympic Games. Finny had fun with this and distributed prizes then.
Also, if you were to date the prizes, they were indeed all period specific to the 1940s.
Finny comes up with the idea of holding a Winter Carnival complete with games such as a ski jump and slalom races. The students set things up on the bank of the river. Brinker brings out jars of hard cider.
The prizes consisted of Finny's icebox which had been stored in the basement, a Webster's Collegiate Dictionary, a set of York barbells, a copy of the Iliad,Brinker's Betty Gable photographs, a lock of hair, a handwoven rope ladder, a forged draft registration card, and $4.18 from the Headmaster's Fund.