While going thru a copy of a "official" Alco specification list, I came across several Alcos with proposed spec numbers that were never built.
DL-428 2750 hp
DL-442 1200 hp w/6-251
DL-450 1200 hp w/8-251
DL-650 5000 hp w/2 16-251B
DL-702 Model RS-38 1800 hp
DL-703 Model RS-14 1600 12-244 4 axle
DL-722A Model 620 2000 hp 12-251 6 axle
DL-810 RS-21 1000 hp MLW only
DL-840 Model RD-1 4000 hp (2) 12-251
DL-1730 SSB-1 1320 hp (2) 6-539 2 units
DL 1740 2000 hp (2) 6-539 2 units
DL-1671 RSX-22 1800 hp 12-251 6-axle for military
DL 1650 RS-1 6-241 for testing only
DL-428 2750 hp
DL-442 1200 hp w/6-251
DL-450 1200 hp w/8-251
DL-650 5000 hp w/2 16-251B
DL-702 Model RS-38 1800 hp
DL-703 Model RS-14 1600 12-244 4 axle
DL-722A Model 620 2000 hp 12-251 6 axle
DL-810 RS-21 1000 hp MLW only
DL-840 Model RD-1 4000 hp (2) 12-251
DL-1730 SSB-1 1320 hp (2) 6-539 2 units
DL 1740 2000 hp (2) 6-539 2 units
DL-1671 RSX-22 1800 hp 12-251 6-axle for military
DL 1650 RS-1 6-241 for testing only