Hello Les & Cliff,
I have found a photo of a very similar mobile concrete mixer in action in the following website
http://www.ibiblio.org/hyperwar/USA/...istics1-6.html
It shows a truck reversing up to one of these machines delivering the aggregates.
If you look at the photo it has the same type of central wire pulley to lift the scoop that is lying on the ground, and into which the truck is tipping.
The one in the picture here is probably a slightly bigger version than that landing froom the LST, but it has a very similar undercarriage with the same padded tracks which are needed to avoid damaging the underlying lean mix concrete subbase.
Regards
Nick Balmer