[lbrachfe]

Newell uses a Monoblock design that can be found in many applications including home radiant heat systems. I'm sure that any 4 port with the same size inlet and outlet would serve as a fine replacement. The heated coolant needs to flow through 45' hoses to the front heater core and then return 45' to the engine compartment and that's a long way, but as others have posted after driving it's plenty hot from the engine circulation.
Richard, you may have a blockage or as was previously suggested you may have the valve turned down or closed on one of the four ports on the Monoblock... I cleaned and tightened it all up at the Newell Factory when my radiator was replaced and it was simple to do , but not the easiest place to get your hands around.