Thanks for the replies. I thought I installed the NOS one correctly - I don't recall fighting anything when putting it on. And I don't recall having an issue putting on implements, the arms were level with each other through the range of motion (the implement was always level), and there was never any binding.
It's possible the bush hog hits the ground sometimes, but I'm not leaving furrows in the ground, except with the link broke. My ground is relatively flat with holes from animals, no rocks sticking up, and I've taken care of all stumps long ago with a stump grinder. I'm pretty good about not hitting things with the tail wheel - I've taken out some barbed wire fence and small tree once, about a decade ago.
The reason I was under the impression it was cast was when I described the break to a weld shop, that since it was a shear break it was cast. I've never welded. I think I'll find a well shop to fix the original.
I've got the same concern about the additional torque on the arm, the adjustable link sits an inch or two further out than the original one.
Concerning the adjustable link from Agrisupply, the length on the one I bought seems to be correct. There is a bit of an angle on the bottom (you can't really tell in the photo) which may be less than the Agrisupply angle. But the again, both are photos and it's difficult to tell.
The bush hog does have a flexible top link, I don't think the tiller or bottom plow does, and I'm sure the log splitter doesn't.