Goofy thought, but I wonder if an OD unit off the 3 spd Man trans would bolt to an A/T??? We know Ford never made an OVD automatic in those years.
One of the popular "add on's" for the street rod guys is the Gearvendors Overdrive. It replaces the tailshaft. They were widely used in motorhomes before all of em came w/OVD.
It would actually give you a 6 speed. 3 direct and 3 over. If you had 3.73's or 3.55's you'd have the best of all worlds. Quick around town acceleration and sweet smooth overdrive for the freeway. Go down the road at 75 taching 2500?? Prob get 20 mpg too.
1960 Convertible (Orig owner)