Maybe it should be noted, in addition to Denny's comments, that the new-design 1954 rear-engine cross-member allowed 3 and 4 speed transmissions to be mounted without a rear-of-transmission mount, eliminating the the frame cross member for a rear-of-transmission support with either manual transmissions.
The new (Chevrolet truck) Hydra-Matic was introduced in 1954, and it required a rear-of-transmission mount on a removable frame cross member (only used with Hydra-Matic transmissions).
GMC had a domestic truck Hydra-Matic transmission in 1952 on one model, and a H-M transmission option on all light/medium trucks in 1953 - both years/transmissions using the old style rear-engine cross-member (and, of course, a rear-of-transmission mount and cross-member).
