No, My 300 is in an '85 E150, not the early model. My 289 was in a Mustang.
What I'm saying is the 289 or 302 with the right cam and carb will run real nice at low rpm. It won't have the off idle torque of the 300, but it will come to life at 2200 rpm or so.
In a vehicle the weight of the early Econoline, I would think you'd be very happy with a 289 or 302.
And you won't have to do some unsightly sheet metal mods to wedge it in there.