a quick note:
modern EMD locos
GP: general purpose, 4 axles
SD: special duty, 6 axles
SW: switcher, 4 axles
MP: road switcher, 4 axles
the number in almost all newer EMD locos is just the model number. the -2 at the end means the locomotive has been upgraded with dash 2 electronics. if it has a T in it, like SD45T-2 or SD40T-2, it is a tunnel motor locomotive, the kind with the big air intake screens at walkway level on the rear. if it has AC in the name, like GP38AC, SD90MAC or MP15AC, it runs on AC power instead of DC. if the locomotive has a wide cab, it usually has the M letter in the name, like SD90MAC and SD70M.
so, a SD90MAC is a six axle, series 90 locomotive, with a wide cab, that works on AC power. and a GP39-2 is a 4 axel, 39 series locomotive with dash 2 electronics.
GE locomotives:
B: 4 axle
C: 6 axle
with GE locomotives, the number in the name is the horsepower rating. then they have the - numbers at the end, like B23-7, C40-8 and C44-9. those numbers designate different upgrades in electronics and other things that were made through the years. GE uses the W designation for widecab locomotives, and the AC designation for AC powered locomotives. then there is the older U series locomotives. the best way to tell the difference between the U series and the dash series of locomotives is that the -7, -8, and -9 series and the newer stuff have a radiator on the rear that overhangs the walkway, kinda looks like wings.
so a C44-9W is a 6 axel locomotive, 4,400 horsepower, dash 9 components, with a wide cab. and a B23-7 is a 4 axel locomotive, 2300 horsepower, and dash 7 components, with a regular cab. a U23B is a U series, with 2300 hp, and 4 axles. then you have the really new stuff, like the ES44AC, it is an evolution series, 4400hp, ac power.
both makers stopped using the M designation because every new locomotives they make now have a wide cab (SD70ACe, C60AC, ES44DC)
and to confuse things even more, some railroads use different designations for the same GE locomotives. you might see a GE labeled as a C40-8 or an 8-40C, or CW44AC as AC4400 (union Pacific also has a C44ACCTE the CTE is a special type of traction control electronics).
i really don't know anything about Alcos or Baldwin diesels, but most of them are gone anyway.
hope this didn't confuse y'all any more than necessary