Do you mean the push-button shifter like in my 64 Valiant? Imperial Services sells a kit to convert the cable-shifter to actuate a later TorqueFlite lever shift, but pricey ($180). Looks like could fab anything yourself, so maybe use if for ideas. The M-B shifter is a lever, but rotates about a horizontal axis (Mopar's about vertical axis). At least both are on the driver's side, so the cable should reach.

Amazing work, especially the custom frame. The front strut suspension also looks non-Dodge truck. I am guessing you like the show WelderUp on Velocity where they do rat rods and monster diesels.