'23 was the original proposal that was voted down. B&O's original class M26 (no suffix) was built to that spec, but everything else was derived from the revised '24 specs.
As for the RC kits, 7002 is the original X29 from 1924 (also B&O M26B).
7001 is the revised rivet pattern for the side sheets, plus the Dreadnaught ends used on the X29s built in the early 1930s. Kitbashing the plate ends from 7002 onto 7001 will get you a late '20s X29.
7003 is the ARA 1924 design (B&O M26A, C, D, etc. and not the same as the early X29).