I think the engine is getting to the right temp. The heater core is probably full of DexCool crap from when the orange coolant was in there. Try Disconnecting both heater hoses and back-flushing it. If you get good flow you will need to check the baffle door next to the heater core under the dash.
If all of this is okay then you can obstruct 1/2 of the radiator with a piece of cardboard. This is a temoprary fix but you will get heat. Many semi-trucks do this every winter, they just have snap on vinyl covers.
Good Luck.