Table:
text: Northern Pacific Railway locomotives
Mallet and Simple Articulated Locomotives
Mallet and Simple Articulated Locomotives
Class_ Wheel_arrangement Fleet_numbers Manufacturer Serial_numbers Year_made Quantity_made Quantity_preserved
Z-6 4-6-6-4 5100–5120 Alco 68760–68780 1936–1937 21 0
Z-7 4-6-6-4 5121–5126 Alco 69540–69545 1941 6 0
Z-8 4-6-6-4 5130–5149 Alco 70143…71962 1943–44 20 0

Question: Which manufacturer has a 4-6-6-4 axle arrangement and a z-7 class among Northern Pacific Railway's mallet and simple articulated locomotives?