Update.

Yesterday I tried the garden hose solution and....it worked!!!! First
I disconnected the bottom heater core hose at the heater core and the
upper heater core hose at the back of the thermostat/distributer
housing. Very little water came out. I put a funnel on the top heater
hose and poured CLR through it. It cam out of the bottom exit of the
heater core just about as fast as I poured it in. Next I connected the
garden hose to the top hose of the heater core using a garden hose
repair coupler. It urned it on and clear water came out of the other
end. Here comes the interseting part: I then reconnected the bottom
hose of the heater core at the core and removed it from the other end.
I connected the garden hose to it (the bottom heater core hose) and
turned on the water. The garden hose loaded up and very little dirty
water came out of the top hose of the heater core. So I turned up the
water on the garden hose to it's limit and placed my thumb over the
exit of the top heater core hose. I let preasure build up and I
removed my thumb. Water would spurt out and return to a a very small
flow. However, after doing it over and over again about five times, it
seemed like a cork popped out and  the water started shooting out full
blast. Nice clear water. I then hooked up both heater core hoses,
turned on the car, let it reach operating tempature, and...... some
heat! Just a little. However, when I drove the car the heat became
much stronger.

I next want to do a full coolant system flush. I imagine there must be
all sorts of junk in th system. Can anyone suggest the best way to do
a flush?