The part from the heater hose is the cut-off valve for the heater core. Only the SUVs had it on the old body style. It uses vacuum controlled by the AC unit to shut off the flow to the heater core when the AC is in use. You can eliminate it or plumb it into your new heater lines. You would have to add the vac lines to the intake if you want to use it and there should be a solenoid that attaches to it on the vac line.
I would just ditch it, like I said before, none of the trucks had it only the SUVs. That part is prone to develop leaks too.