I've heard it rumored, and people have said they've done it, but I never saw any pictures of what a tonneau cover or cap for the 8' bed of a Dodge Dakota would look like on a J-truck.
So i bought a TruXport TruXedo #242-601 tonneau for an '87-'96 Dodge Dakota with the 8' bed. It seems TruXport just recently discontinued this model, so a number of orders through Amazon were backordered, or the wrong item shipped, or were just cancelled. Finally I got a new, in-box version off a seller on e-bay, and installed it today. It does fit, though I will need stake-pocket plugs to make it really weather-tight.
I made a video of the whole install as proof:
https://youtu.be/zzTwWQpzhyw