When we first got the Yellow Submarine the door latch was heavily rusted with the chrome pealing off. and the key was not functional. We purchased a new latch from the local Kenworth dealer for about $32 and a new key cylinder for another $22 Actually we got 2 cylinders for that price.
The new Kenworth latch did not match the original in that it did not have the appropriate appendage to attach the inside door release handle. The remedy was to cut a small piece from 12 ga sheet metal, drill a hole for the actuator arm and welded it to one appropriate arm on the new latch such that it functionally resembled the original. My original though had been to bolt the new appendage to the new latch but found the parts in the new latch were hardened steel and my drill bits would not touch it. The new modified latch bolted right in and works great, the only down side is that I now have a Kenworth key to open the door then the typical GMC entry key.
The following picture is of the modified latch after it has been in successful service for several months and has been removed to paint the coach. Because this was an early 73 coach it is mounted on a stainless plate since these latches were put on after the original latch was determined unreliable. The plat covers the original hole so this style of latch can be mounted.