I also think the vehicle is a Crossley with Kegresse gear fitted to the rear but have so far been unable to locate any comparison. The closest that I have come is the header photo on this link which shows a very similar vehicle, also at Seletar, around the same time.
2006 June « Seletar Airbase project
Can't really tell from that photo if there is a double front wheel arrangement.
The front wheels of the vehicle in the original photo that I posted seem to be a more permanent fixture than just added axles for crossing rough terrain. That is a possibility though.
I have just found a site that deals with the historic aspects of Crossley vehicles and am about contact them for advice.
I attach the second photo that I have been sent below. It was taken further away from the subject and shows a little more of the scene. I have cropped in a little to try and show more detail.
Vildebeeste down-12 by
Janner88, on Flickr