The shop manual specifies fuel pressure of 4 to 6 psi, and an unrestricted flow rate of 1 pint per 30 seconds or faster, and stresses the need for pressure to be in correct range. You likely need a pressure gauge to check it.
I also have a 1965 Econoline with a 240 and an electric fuel pump. My pump is the "Mr Gasket" available from Autozone for about $45. And the engine seems to be running a bit rich. The pump claims pressure to be in 4 - 7 psi range, but who knows what voltage they applied to the pump when testing it.
When I finish other tasks that are preventing me from passing inspection (I wanna get it on the road!!!), I may try dropping the voltage on the pump a little to see if that helps; a resistor is probably cheaper than a pressure regulator.