Ford built jeeps with functionally interchangeable parts and components, in part facilitated by using components from common sources: frames from Midland Steel, wheels from Kelsey-Hayes, and axles and transfer-cases from Spicer. However, there were many minor differences; the most well known: the Ford chassis had an inverted U-shaped front cross member instead of a tubular bar, and a Ford script letter "F" was stamped onto many small parts. Many body detail differences remained for as long as January 1944, when a composite body, fabricated by American Central, was adopted by both Ford and Willys. It integrated features of both designs. Through the chaotic circumstances of war, sometimes peculiar deviations from regular mass-production came off the assembly line, that are now prized by collectors. For instance: the earliest Ford GPWs had a Willys design frame, and in late-1943, some GPWs came with an unmodified Willys body; and in 1945 Willys produced some MBs with a deep mud exhaust system, vacuum windshield wipers, and a Jeep CJ-style parking brake.