How many designs of AC locomotive (diesels only) exist for narrow gauge worldwide? I know of three: Japanese DF200 (introduced 1992), Bombardier/GE DE-AC33C "Blue Tiger" (introduced 1996), Clyde-EMD GT42CU-AC (introduced 1999).
Fan of late and early Conrail... also transition-era PRR, 70s Santa Fe, BN and SP, 70s-80s eastern CN, pre-merger-era UP, heavy electric operations in general, dieselized narrow gauge, transition-era DB and DR, modern EFVM and Brazilian railroads in general... why bother trying to list them all?