oldieoldie,
This info may be of help.
Attached is a screenshot from a GMwiki parts search. The 6400 is identified as "Utility" in the part model application list.
List shows 35-57 Utility - front and rear brake shoe locking clips (1-3/16" OD) GM# 359380
Chevs of the 40's lists a 1-3/16" Huck brake shoe retaining clip set (2 per set) here:
https://www.chevsofthe40s.com/detail/6301/Chevrolet_Brake_Pin_Lock_Brake_Pin_1316_OD.htmlDescription does not say that it includes 6400 2-ton vehicles, but size matches whats listed in the Master Parts book. At less than $10 per set (no idea what shipping is) maybe worth ordering to check out.
Let us know what you figure out.
