Here is the OFFICIAL NUMBERING SYSTEM for all of SOUTHERN ATLANTIC TRANSPORTATION and J&S RAILWAYS.
Deisel Number system
001-099....................Yard and road slugs, also "B" units.
100-199.........Yard locomotives. Primarily switch engines.
200-299......Heavy yard locomotives consisting of 6 axles.
300-399..................................Road haul locomotives.
400-499......Road switchers.
500-599......Passenger Locomotives
600-699......Industrial switchers.
700-799......Locomotives for lease.
800-899......Test or new locomotive designs.
900-999......AC powered locomotives.
STEAM LOCOMOTIVES
0-4-0........400 series
0-6-0........600 series
0-8-0........800 series
2-8-0........2800 series
2-8-2........2820 series
2-8-4........2840 series
4-6-2........4620 series
4-6-4........4640 series
4-8-4........4840 series