Mike, if you're repairing an original '26 Gibson Ballbearing neck, the lower lag screw is actually an L-shaped lug that is embedded in the heel of the neck and which is threaded for the older style coordinator rod...
Those are difficult to find if you want to replace with the same kind of L-shaped lug. You would probably have to fabricate it. And replacing it in the original neck means doing surgery on the heel.
If the neck is a newer 3rd party neck, it probably has a modern lug arrangement which will be easier to find and easier to install. Just make sure the threads are correct for the original old-style coordinator rods.
Good luck with this!