Base lock mount

Sounds like you need a keeper for the mortise lock. I recognize your mortise, but the bad news is that this is compatible with about a half million different keeper styles. There's not just one part that works with this. Since you're missing the original, we have no way of knowing what size you actually need. Depth is a very important factor when it comes to this kind of thing.

For now all I can do is list our most popular keepers that pair with this mortise. See our 89-020, 89-021, and 89-021D. Your only option to determine the right size is going to be trial and error.