Hi Guys:
I couldn't get good enough definition on blow up but I'd bet that the tractor in the 1950 picture is a Ford LAAT. Definitive would be a good look at the front bumper for the winch fairlead, the hand crank support and the brush guard mounts. On the body look for the horizontal handles that open the lockers for tools and ammo.
Interesting to note that the spare is on the roof... CMP roofs aren't that solid... the weight of the air sentry hatches caused them to buckle, let alone 200 lbs of 11:00X20 tyre and rim!
Round roof hatch points to late production and, if we can get confirmation on the LAAT body, would be a relatively rare thing as not many LAATs got the hatches. I guess they figured that bird gunners would be doing air sentry with the Bofors not with a .303 girlie gun.
Cheers! Mike