George,
You are partially right. Ford began building it's own 1/2 & 3/4 ton 4x4's in 1959.

Before that, they were converted by an external company (Marmon-Herrington) and sold through the dealer or a 'kit' could be purchased from Marmon-Herrington by a dealer (to be installed by the dealer). This conversion process worked much the same as it still does for ambulances, hearses, early crew cabs, schoolbusses and other special body styles. Marmon-Herrington continued building F-350 and larger 4x4's until a later date (possibly '64 ?? anybody else know?) I think they still do Ford's conversions on 3-ton and larger trucks.

Ford mechanics still had to maintain these. Unlike body conversions authorized mechanical conversions (4x4) were documented so that they could be repaired. Even as NumberDummy (THE Ford Parts God around here) has said the official books list the NP203 & NP205 as the only transfer cases used. This is simply not true. The text and pictures don't match, if you read up further you'll find a link to an exploded view dated '74 that IS a Dana/Spicer 24, but it's not labeled as Dana/Spicer part. I stand by my statement that Ford created this confusion.

Jim

ps: NumberDummy you rock !! Unfortunately, not all parts guys are created equal and some believe those parts books were chiseled on stone tablets by the infallible hand of Henry Ford himself. A parts manager near me came just short of calling me a moron because tried to get parts for this "non-existant" transfer case. ND, your efforts have helped me and many, many, MANY others get info we never would have found ourselves. And the internet preserves this info for others who will hopefully continue to fix, rebuild and play with our toys long after we're dust.