Ron,
Are you collecting all steamers Pennsy built starting from the 1860s? That would be really neat.
I was concentrating only on engines the Pennsy had in operation in 1949, which included both the N1s and N2sa (I've already broke this rule with the Y3, and going to again with the Q1 and S2).
The N2s, a USRA design, would probably be more cost effective for one of the model manufacturers to build since other railroads used it too. However, a PRR N2s being gone by the mid-1920s would not fit into my layout theme.