After taking parts out of the way under the dash and tracing control cables, I find the heater problem is not as bad as it looked at first. The defroster distribution and control comes from a box on the other side of the cab that is over the accelerator pedal. What is missing is about 3 feet of large ducting that moves air from the blower to the distribution box and the piece connecting to the blower that converts the square exit to a round duct. I can make this if it can't be found elsewhere.

I am still looking for a heater core and will put up another post about this because I can't be the first truck owner looking for a larger than standard core.

JRMunn