"Did a 3800 come with a fendered stepside bed on it? I would have assumed those trucks were sold as a cab and chassis only."

1950? if a pickup bed - all were "stepside" (a 1-ton cab/chassis model was also available)

1966? a stepside and fleetside 3800 pickup was available

year in your question? 1950 4100 = it looks like none of them came with rear fenders?