Yep, I'm 99.9% sure that one is the right OEM cable for you.
Check this out. This is for 6.9 E250 and 350 6.9. It should be the same for a 91 E250 and E350 7.3, I would imagine.
Note the part number of the cable assembly it shows, 9A758:
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Now let's look back to that interchange list:
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That part number is interchagable for the Pioneer and ATP ones:
https://www.rockauto.com/en/moreinfo.php?pk=5898654&cc=1117448&jsn=9
https://www.rockauto.com/en/moreinfo.php?pk=65247&cc=1117448&jsn=8
And those are the ones that fit a 91 E350 7.3:
https://www.rockauto.com/en/catalog...iesel,1117448,interior,accelerator+cable,5892
We know that part on ebay is for 87-89 6.9 E350 vans and an 87-89 calls for the same ATP and Pioneer cables for your 91, so I seriously see no reason why it wouldn't fit.
You might try submitting a best offer to that ebay seller if you really want an OEM cable since they are accepting them. And no, I'm not the seller. I'd be keeping that thing as a backup if I had it.