If you're a Pennsy fan, you can only have one of the two Kato NW2's on your layout, depending on the date you model. The PRR's second purchased Diesel was NW2 no. 3909, bought in October 1941. It's first was 3908, an SW1, bought in 1938. In 1942, 3909 was renumbered to 5912, so both numbers never appeared on an NW2...
The lower 3900 series numbers were used on A6's, distillate and Diesel 0-4-0 boxcabs built by the PRR as early as 1928. Might just have to get a 3909 for my roster...