Eric: HP is a function of RPM, which, yes, is a governor setting:
B series 800 rpm maximum governed speed
C series 835 rpm maximum governed speed
6-567B 600 hp SW1
8-567B 800 hp SW8
12-567B 1000 hp NW2, SW7, E7
16-567B 1350 hp F2
16-567B 1500 hp F3, F7, GP7, SD7
6-567C 600 hp never offered in a locomotive that I know of, only stationary apps.
8-567C 900 hp SW900
12-567C 1200 hp: SW9, SW1200, E8, E9
16-567C 1750 hp: F9, GP9, SD9
A BC engine is identical in performance to a B engine but has the C liners. There’s also an AC engine, which is the A crankcase with C liners. I never saw one, but the EMD unit exchange catalog lists them. And lastly a 645C or a 645BC, which is the 645 liners in a C or BC block, at the old horsepower rating. You could also put a D liner in the C block; the Rio Grande liked that because it had bigger ports and ran better in the thin air of high altitudes.
Some railroads knocked back the C engines to 800 rpm to increase longevity – a machinist told me that at 800 rpm the C engine ran forever, but at 835 rpm they tended to come apart too often.
Beyond this starts myriad variations. My 1982 unit exchange catalog lists, for instance, 59 different models of governors: that’s why more than one person in the shops will tell you that EMD stands for “Every Model Different.”
As for what’s rebuilt and what’s remanufactured, it’s basically whether you’re recapitalizing the unit or not. As far as I understand the regulations, you can fix a 567 forever and never have to upgrade. But it won’t matter because the 567 is vanishing very quickly because it’s so much cheaper to buy a used 645-engined locomotive than to fix the 567. You can go buy a good running SD40-2 for less money than it will cost you to rebuild a GP9 – I’ve seen the former offered with good wheels under it for $60,000! Ten years ago the same SD40-2 was $350,000. That’s w