The 3-rail NYC Dreyfuss Hudson was limited to a production of 750 units. Item# 6-18027 and 6-18029 with roller base# 6-23001
The 2-rail NYC Dreyfuss Hudson was limited to a production of 500 units. Item# 6-18026 with roller base# 6-23000
The 2-rail PRR K-4 Pacific was limited to a production of 300 units. Item# 6-18028 with roller base.
The roller base may be the same as the 2-rail Hudson. I am not sure about that fact.