A Kingpin set for a certain Dodge truck from about the early 60s will work in a ZAS. The taper pin groove in the Dodge kit is different but you can grind it deeper and it will work.
I'm thinking those kingpins are only 1-1/4, though.
When I was looking for axle bushings for a Cub Cadet Original I found some steel backed bushings at McMaster Carr website that I thought would work as kingpin bushings, but they were not cheap, though. On the other hand, that's probably a job you only have to do every 50 years or so. (If you know what grease is. . .)