Just to add a little something to the Australian rail-car convo, here’s a couple of snaps I took of a '30s NSW ‘Rail Pay Bus’. Originally designed and built by Waddington (Granville, Sydney) in the 30s as railbuses for use on branch lines in Central Western NSW, these had petrol powered 221cu in (3.6l) Ford V8s and were built on truck chassis. The experiment failed and all six were converted for use as paymaster’s vans, and apparently were used all over the NSW rail network right up till the late 60s.
Photos taken at the NSW Rail Museum at Thirlmere (NSW), a place well worth a visit if you’re in that neck of the woods, especially on Steam Days.