One design, two makers, a synthesis nobody built alone

There was no trim hierarchy — this was a single-configuration military contract vehicle. The meaningful variation is by maker and production date: Willys used a welded-grate grille through unit 25,808, then adopted Ford's 9-slot stamped-steel design; a composite body (fabricated by American Central Manufacturing) finally unified remaining Ford/Willys body details starting January 1944. See /rare-and-significant for the slat-grille MB (the earliest ~25,808 units) as its own identification subject.

The fastest field test for MB vs. GPW: the front frame crossmember under the radiator is square on a Ford GPW, round on a Willys MB — useful because bodies, engines, and frames were swapped between the two by the military itself, especially after the war. Two ID plates carried the same serial from the factory (left front frame rail, firewall under the hood); a separate body-tub number lives in the left toe-board gusset and can disagree with the chassis serial on a rebuilt vehicle. Willys and Ford used non-interchangeable stamp systems — see /buyer-guide and /identification for the full authenticity-diligence workflow, and /engines for the Go Devil's role in why Willys won the contract at all.