Cropped from Collection of New York Central System Historical Society, Inc., No 7347-4

In 1920-1921, the New York Central constructed two different, adapted versions of the never built USRA steel box car. The first was nearly an exact copy of the USRA design consisting of 1,500 box cars and 250 auto cars, constructed by Standard Steel Car Co. The other design was much closer to the 1916 steel box cars that the New York Central built in significant numbers. This version consisted of 2,250 auto cars built by American Car & Foundry. However, in 1922 the NYC developed a different variant that would become its standard box car for the next decade. It was known as Specification 486. In addition to the 2,500 auto cars built as "prototypes" by SSC and AC&F (and referenced above) the New York Central built an additional 4,000 to an 8'7" IH and another 3,000 to a 9'4" IH, both types to Specification 486. The information about all of these cars is listed in the following table:

New York Central USRA Steel Auto Cars
"Prototypes" and Production Variants

Road	Lot	Builder	Year	Series Start	Series End	No. Blt.	Notes
NYC	416-B	SSC-H	1921	116000	116249	250	42 cars converted to box cars by temporarily securing auxuliary doors, assigned to 188000-189299; 182 cars reclassified to box cars with no change to doors, assigned nos. 144000-144249; 241 cars converted to box cars by relocating door post and applying 6' doors, assigned to Lot 803-B with nos. 30500-30740
NYC	417-B	AC&F	1920-1	116250	116999	750	Fishbelly center sill underframe; 88 cars converted to box cars by temporarily securing auxuliary doors, assigned to 188000-189299; 182 cars reclassified to box cars with no change to doors, assigned nos. 144250-145599; 1771 cars converted to box cars by relocating door post and applying 6' doors, assigned to Lots 659-B (131000-131999), 696-B (135200-135699) and 718-B (135700-136214)
MC	418-B	AC&F	1921	94000	94999	1000
CCC&St.L	419-B	H&B	1921	90186	90685	500
MC	440-B	SSC-H	1922-3	96000	97999	2000	389 cars converted to box cars by temporarily securing auxuliary doors, assigned to 189300-190999; From 1930-2, 1500 cars had IH increased to 10'0", nos. 194000-195498; 388 of 10'0" IH cars converted to 6' door box cars, Lot 806-B assigned, nos. 31000-31099 (conv. at Beech Grove shops) 31100-31387 (conv. at East Buffalo shops); 2500 cars converted to 6' door cars with no height increase, Lots 627-B (MC 84000-84999) 804-B (NYC 29000-29749 [conv. at Beech Grove], 29750-30499 [conv. at East Buffalo]); Cars that remined as originally built assigned to series NYC 145400-146999.
MC	464-B	ACF	1923	98000	99499	1500
MC	465-B	SSC-H	1923	95000	95499	500
NYC	493-B	PSC	1924	52000	52999	1000	9'4" IH; 442 cars converted to box cars by temporarily securing auxuliary doors, assigned to 191000-193999; 1422 cars reclassified to box cars with no change to doors, assigned nos. 147000-149999; 60 cars from Lot 493-B have floors reinforced for handling sheet metal coils; 2956 cars converted to box cars by relocating door post and applying 6' doors, assigned to Lot 805-B, nos. NYC 34400-35899 (conv. at Beech Grove) & 35900-35900-37399 (conv. at East Buffalo)
MC	494-B	SSC-H	1924	86000	86999	1000
MC	536-B	SSC-B	1926	85000	85999	1000

ACF - American Car & Foundry, St. Louis
H&B - Haskell & Barker, Michigan City, IN
PSC - Pressed Steel Car, Hegewisch,
SSC-B - Standard Steel Car, Butler, PA
SSC-H - Standard Steel Car, Hammond, IN

References:
Westerfield Data Sheets for Series 2900 & 3000 kits
Dimensions & Classification of Freight Car Equipment of the New York Central System, December 31, 1938 (revised June 30, 1944) and January 1, 1954