The only other option besides welding, that would probably be safe and strong enough for regular use, would possibly be to get/make another bracket with the ball stud, and bolt it onto the same place, using something like a 1/8" thick and 1 inch wide flat steel strip on the back side (inside the liftgate) with two bolts welded through it, that would then sandwich the liftgate sheet metal, with metal locknuts on the outside.
This was my idea for a repair when one of the supports finally came off mine. It'd be a little tricky to do with the liftgate on the vehicle, since you'd have to stick the metal piece up there and somehow get it the two bolts through the bracket holes, but it'd be doable with a coathanger method or magnets and enough time. I think part of the reason I didn't go with this is that it looked like there would not be enough clearance for the gas struts/cylinders when using nuts - and there would be the risk of having the nuts/bolts in contact with the gas cylinder when closed, eventually leading to a puncture and possibly some other catastrophe when the liftgate was next opened. It might work with some low-profile nuts or using a tap to thread the holes in the metal strip and putting a lot more time into positioning the strip inside the tailgate while trying to bolt the bracket on.
Of course, if you have a welder to weld bolts to a piece of steel you might as well weld new brackets to the liftgate, but if you don't trust anyone welding the liftgate, you can just have them weld the new hardware. I welded the bracket back to the liftgate and it works great.
You could also just rivet a new bracket in place, and rivet an additional thin metal strip on top of that, (which is exactly what the recall repair kit was), but you'd probably want to take it a little bit easier on the liftgate when opening and closing from then on.
Even just tack welding the riveted new bracket in a few spots would add quite a bit of support and keep the load from just being on the riveted points. I welded the whole thing after sticking a piece of metal on the back, so it should last another 20+ years.
It's a shame Ford didn't make the brackets bolt-on with reinforcements at those points on the liftgate, would have made things a lot easier.
EDIT: If
just the ball stud is missing (as in the ball rusted apart and the backing stud is still in there), and the
entire bracket is still in one piece, you just can just drill out the rest of the old stud, and replace it with new ones:
http://www.autozone.com/autozone/accessories/MightyLift-Stud-kit/_/N-255s?itemIdentifier=209378
You may have to trim the threaded end to fit, or maybe just using a washer on both sides will give enough space. Seems they sell 10mm and 13mm studs, so you should probably measure to be sure you get the right size. I'd guess most auto parts stores would have these.
Either way, cheap and easy fix compared to messing with new brackets.
You may still want to rivet metal straps to the brackets though, just for support, to prevent having them tear off and avoid needing to weld/repair them in the future.
