These two vans (Z6785 and Z6789) were converted from AS class six-wheeled mail vans AS253 and AS252 in 1906. The other AS became Z6790 later Z109. At least according to the WAGR outline diagram below, they retained their clerestory roofs at first unlike Z6790. They had 4'-10" bogies and were 32'-0" long. Z108 at least was later rebuilt with a body very similar to a type 7 van. This probably indicates that the rebuild happened at about the same time as the type 7 vans were being built (i.e. about 1910-1920). Despite being written off in 1968, Z108 survived until at least 1984 within the confines of Midland workshops where the photo below was taken.  I don't know if it got a Jetty Stock number.