Based on that last picture I don't even know if I'd want to fix the carrier. Kinda why I would look for a donor, I think the 2nd gen Dakota's were '97-'04, so at worst any of those quad cabs should work. The rails don't look as bad as the carrier, but if I was going to remove a carrier at a wrecking yard I'd just remove the rear bed mounts and springs and take the whole back section of frame, be a lot faster than dealing with the rivets.
Not saying you can't fix the carrier, I just don't think I'd want to mess with it. Even if it's quad-cab specific there's more of those than A-body donors, and guys find those still.
Does the tire carrier/crossmember locate anything other than that shock mount? Heck I'd be more inclined to get some 2"x2" square tubing and build a new crossmember compared to trying to repair that one. Again, I'm not looking at it in person, but it looks rough. Just cleaning it up enough to run good welds might take longer than building a new one out of square tubing. Options I guess.
