Welcome back Golfball! It's been a long time between posts.

Craig is right about posting an ad in the Swap meet's
Truck Parts Wanted forum to see if someone can help you out on where to find a replacement shifter.
As to further details about "are these specific to the AD trucks?" and such, here's some info from pertinent Chevy Master Parts Books to help answer those questions.
A picture of the shifter handle and component break down is attached below from a
1929-57 Chevrolet Master Parts Catalog. Looking at the major component items that make up the shifter, Parts Group 4.006 - Lever assembly, shows that the same part number GM# 3686799 applies to all Commercial Trucks from 1948-53 and 1949-52 Chevy Passenger Cars.
So either range of vehicles can be a donor for the shifter parts you need.
Armed with this info, get that ad up in the Swap Meet and we can further help track down what you need.
EDIT NOTE - See corrected information below as this applies to 1953 and earlier trucks, not Golfball's '54. 