gotta love these machines that havn't been maintained very well...
nice and gunky... ugggh

anyways from those pics i see that first pic of the housing up near the top on the side that has the sensor beside it appears to be the thermostat housing. My guess is if there was no thermostat in it, that someone has removed it at some point in the past. If that flange has a machined out groove like most theromstat housings do this is where the thermostat would normally seat when in place.

The hose that runs from under that housing down to the side of the engine block beside the waterpump? It looks to be someone put a regular (non-molded) hose there, hence the reason for the kink in it, it doesn't look normal to me. I'll also assume that hose running to the LP regular taps into the side of the housing where the theromstat is? That would be the bypass circuit i mentioned earlier. It should run to one side of the regulator and then out the other side and tap back into the system at another point probably around the intake manifold?

I would make sure that bypass circuit is clear.
From the looks of the pic's though the inside of it looks fairly clean.

Before you took this apart did you run the truck and check for circulation?