What is the problem with what you have? Does it have some small holes that are leaking because someone took the valve out? If so, you can put bolts in them to plug them. If you have a friendly parts person, they may be able to find a spacer for you, or a whole manifold that didn't have the heat riser. I am not sure, but suspect there may be a factory setup that didn't have the heat riser system, but finding it in the parts book will take some time.
P.S. I think I know what the problem is; Is the mounting ear broke off in the picture?
On the '85 F150 I parted the heat riser was on the driver's side. Don't know about an F250, but I think it would be unusual for Ford to swap sides.
Also, that one doesn't seem to have the shaft nor the butterfly it would have as a heat riser. And, the one's on the F150's had a vacuum motor. So, I'm not sure what it is, but I do yield to Dave's knowledge.
As for exhaust manifolds, I do have a pair from an '82 351W that didn't have the riser, plus the '85 pair with the riser. I could measure them this afternoon to see what the lengths are if need be. And, if there's an interest in either shoot me an email (email@example.com) to discuss, although shipping would be expensive I would think.
Oh yes, please go into User Control Panel and fill out your location. Who knows, you might be in my back yard and I can help you.
Stang's got the answer. Here are some shots, but I apologize for the poor quality:
The top manifold is from an '85 351W HO, while the bottom one is from an '82 351W - both are driver's side. As best as I can tell both the manifolds have the same dimensions, but the '85 is flat where the outlet is while the '82 has the bell to fit the exhaust pipe. The '85 requires the heat riser to get the bell, but the riser is 1" thick so that changes the Y-pipe.
Here's the heat riser, and note that the flange is not broken, but cut off:
So, like Stang said, plug the holes and don't look back.