That does surprise with with an automatic. I would think that must have been a special order. IIRC they were geared on the low side so they still had power to move loads at slower speeds even with the small engine but you probably would not get too many speeding tickets at the top end.
I've always had a soft spot for old trucks large and small.
(In fact call me nuts but I've always thought I would like to have an old dump or flat bed with one of the Detroit 6V or 8V 2-cycle diesels. Always loved the sound of those engines! :bag