If you have an Evans dash control,
Evans Tempcon, Inc - Service Parts
you might be able to find a replacement dash unit in a junk yard. Many trucks used the same dash control unit.
I don't believe that the lines from the engine to the front are prone to failure, more likely a leak at a joint or compressor seal. Your A/C probably uses R-134 as a coolant, it's relatively cheap and the cool air is worth it, in my mind.