K C,
That's what I was thinking. Wish I still had my Haynes Ford Van Manual from those years.
But, according to AutoZone's parts lookup... If it's a 2-Barrel, it's a 351 "Windsor" Small Block, 2-bbl, found in about 30% of the 1978 E350 Vans.
AND... These are their related Notes:
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Carburetor to spacer, spacer to manifold. Exhaust gas recirculation (EGR) included. Set.
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This is the "stack" of parts I noted in my post above. I ended up with ours apart because the engine had a vacuum leak that a carb gasket wouldn't cure. I found that the "Spacer" had rusted to the studs at the holes. When I finally got it apart, I found the Spacer-to-Manifold gasket had blown out. Ran much better with new gaskets AND the stud holes freed up. Before, tightening the stud nuts only tightened Carb to Spacer, not Spacer to Manifold...
So, if the Carb Gasket in Part Number: ES70582 fits the Carb Throttle Plate surface, and the EGR "Spacer" gasket fits the Manifold surface, they have the right Carb and Gasket Set. Only problem is that Missing "Spacer" which held the EGR Valve.
The Carb gasket, which OP already has, is available separately as 60716. The Spacer gasket is also available separately as 60244. And the EGR Gasket's available separately. The three prices add up to about the price of the Set.
Hopefully, the Spacer might be available in a junkyard, but it's been a long time...