Howdy Jamie:
All exhaust manifolds for170/200/250 after '63 are essentially the same in that they have a 2" outlet and use the donut gasket and heat dam for a better seal.
170/200 from '65 to '70 are built heavier with extra gusseting in crack prone areas.
After about '75 the manifolds had extra bungs cast in that were tapped for emmissions stuff. These bulges disrupt flow.
What ever you use, make sure- 1. that it has no cracks, at all, 2. that the mating surfaces are not eroded. 3. That the outlet is a full 2" with no casting flashing or slag protruding inward.
I have heard rumors of some Econoline 250 exhaust manifolds with larger volume. I have never been able to verify that rumor.
That's all I know.
Adios, David