It is not the same as the 1/2 ton, but same for 3/4 ton (Commercial) and up through "Utility" trucks (which includes your 6400). See snapshot below (red arrow indicates your application) from this page CYLINDER ASSEMBLY, Hydraulic Brake Main
A further check of the GM# 5454382 cross references to Dorman M9220. Search that number on the web and you will find a whole bunch of vendors offering it for various prices, some much better than others - LOL.
Hope you find this helpful?
Dan
~ Dan 1951 Chevy 3 window 3100 Follow this story in the DITY Gallery "My Grandpa Carl's Truck and How it Became Mine" 1966 Chevelle (Wife's Hot Rod) | 2013 Chevy Silverado (Current daily driver) US Army MSG Retired (1977-1998) | Com Fac Maint Lead Tech Retired (1998-2021)
