I had a problem similar to this in my 65' wagon. The culprit was the fuel tank itself; I suspect the siphon tube inside the tank had developed a leak near the top. Basically the car would run okay at idle, when fuel demand was not high, and I could it drive it down the road a ways before the float bowls would empty out; the engine would then start cutting out and finally die. If I let the car sit awhile the float bowls would slowly refill from the residual fuel pressure in the line, and I could start up and drive for another couple of minutes. I could only avoid the problem if I kept the tank completely full.

I finally replaced the tank, and have had no more problems at all.

Bill