Can't remember where I got this but I suspect it would be something like Archives New Zealand facebook page or something like that. What I am sure of it is it is one of the small Leyland railcars, probably the "Midland" railcars as they were known in NZ. The impression I got was that Leyland in the UK which was a truck and bus company, and this was in the 1930s, actually did produce standard drivetrains for railbus chassis for people that wanted to build their own railbuses (because essentially that is a description of our early railcars). Photo would be from Hutt shops.
Another Hutt shops photo with several different Leyland based railbuses under construction. To be exact you have a couple of the Wairarapa railcars on the right and something smaller like a Midland over to the left rear.
This is a Fiat railcar and it shows how the Fiat engine was slotted in underneath. The Fiat engine used in these railcars was a six cylinder inline engine arranged to be horizontal so that it would fit underneath the floor of these railcars. This arrangement was similar to the Wairarapa railcars (although the arrangement for them essentially put the a standard design of engine under the cab / baggage compartment floor rather like modern vans or forward control trucks) and a departure from Standards and Vulcans which sacrificed length for a separate engine room.