There was a sheet film version of Tri-X available before 1954. It wasn't very common. Alternatively, he may have used Super-XX (common in the studio) of Super Panchro Press Type B (a common press film of the era, high speed, grainy - Weegee used it a lot). My guess is either Tri-X or Super-XX, because it is a pretty smooth image, as I recall. Tri-X of the era would be significantly grainier than Super-XX. The shot was made with EG&G strobes, which didn't put out the light that modern strobe lighting does. Although he had quite a number of them, speed would have been important.