Besides the Navistar setup, I believe the Chevy / GMC P-vans came with a driveline brake at the end of the trans. The 4 wheel disc versions. I know P-vans are included in the 1 ton section when looking for parts, but they can be a bit bigger than that what with the I beam front axle and all.
The Navistar 4700, which is probably equivalent to a 3 or 4 ton truck, should use the Mico mechanical caliper. Not much force is needed to lockup that driveline. These trucks are powered by a DT466 with an automatic Allison World trans. If you'd like, I could crawl under one and get some part numbers or some pictures. We have a fleet of them where I work.
