Well, Griffin and Howe lists 18 rifles in the 400 serial number range:

403, 417, 420, 429, 433, 444, 448, 450, 451, 453, 457, 459, 470, 478, 479, 481, 495, and 496. These were all used rifles that A&F sold at various times.

It might be worthwhile to ask 'em if any rifles were so marked.