Story around the brakes is that I downloaded one of their master catalogs from 2017 which listed a 1928-1940 kit…like you I didn’t see it on their website.
I emailed them enquiring about kit DB1751B 1928-40 GM1/2-TON (5 x 4 3/4" BOLT CIRCLE) and it’s availability.I got an email response back that the kit was still available but due to some website upgrades the kit hadn’t yet been added back.
You might want to email/call them and ask if they still produce DB1751B.