All Marlin Ballard links are not the same, and I've always thought even when they were new they likely weren't all the exact same. I've taken dozens of them out of guns to compare, and found minor differences among them. I envisioned a worker at the assembly bench with 5-6 bins of different length links, trying one to adjust the levers, and firing pin center. Then moving up or down if needed to adjust the firing pin strike, and lever lockup.
When Jim at Distant Thunder sold links he sold them individually, or in sets of 6 varying .001" difference per link. So you could buy a set and try them until you found one that worked.
But the link isn't always the problem. They're pretty hard material, so usually the screws wear before the link. Often I replace the lever screw alone, and it snaps up fine. But sometimes replacing both link screws and the lever screw is what it needs to tighten the droopy levers.
I don't know of a source for the links, or the screws now. But I'd try Wyoming Armory first, since they may have some, or at least could make them.

The Ballard bitza I'm slowly getting together to utilize a nice .28-30 barrel I found on evilBay an age ago responded nicely to making and fitting an oversize lever pivot screw.