Check the wiring that leads to the distributor to see if it has a broken tachometer signal wire.
We had one of these same 7F models that did this and a broken tach signal wire about 12 inches back from the distributor was the problem.
Apparently the 7F models are wired to be able to run without a tach signal in the cranking mode only, but will die immediately when the key is returned to run mode and a tach signal is absent.
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