NMelo,

All the MB and GPW Military jeeps came with the same part number of the 9" by 1 3/4" brake drums for the wheels. There was an upgrade that came about with the '46 Willys Wagon and pick up trucks where it was deemed needed for the heavier Jeeps. The new drums were 11" by 2" drums. the 11" drums could be easily retrofitted to the earlier jeeps by just installing the brake assemblies. This gave the benefit of adding slight bit more stopping power without having to change out any other components.

https://www.kaiserwillys.com/brake-d...b-gpw-cj-2a-3a
https://www.kaiserwillys.com/brake-d...-station-wagon

The parking brake does have a couple of options depending on the year of production. the '41 - '43 had a band style of brake material that expanded to contact the drum on the rear of the transfer case. The '43 - '51 parking brake was a simpler, brake shoe and actuator set up much like the wheel brakes.

https://www.kaiserwillys.com/diagram...iagrams-mb-gpw