Pretty sure the 3/4 tons use the same box as the 1/2 tons, I know the earlier trucks did. Here are just a few I found.

https://www.classicparts.com/1947-54-Steering-Box-Rebuild-Kit/productinfo/76-911/

https://www.chevsofthe40s.com/dept/Steering/cat/Rebuild+Kits.html