Bryan,
Definitely not. Lehigh acquired 50 of the cars from Pennsy in 1934, but they were phased out and supplemented by first-hand purchases of 65' mill gons by the 1950s. Also, the deco scheme is the early lettering style. These are most certainly steam-era models ... although I'm going to stretch it and include one on my own personal 1950s New Haven freight equipment roster.