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 (janeyandgary@gmail.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.