During the late 50s and early 60s, the 1939 IRT WF Steinways appeared on the 7th Ave. Express trains (2 & 3 lines). As with the R-12s, R-14s, and R-15s in later years, they weren't used in solid trains, but were intermingled with older equipment (presumably older Steinway cars). It seemed to me that the WF cars were used at the ends of the trains to take advantage of the head-end roll signs (I distinctly recall seeing a 7th Ave. express pull into Times Square southbound with "New Lots" prominently displayed between the marker lights).
Even though these WF cars had head end roll signs, the side destination signs where of the metal-plate variety.