A neat project! IMO you should leave the 219 safety alone and not get caught up in multiple "belt-and-suspenders" systems like T-C did with their break-open stalking rifle, the TCR-83, etc. One good safety is plenty.
I'm not sure if the rifle's auto ejector needs to be retained, tho. Most single shot rifle nuts are reloaders and don't like to spend time chasing brass down with the chiggers! Apparently that's why you can "turn off" the auto ejector on Ruger #1s, and mine have never been "on"! An auto ejector is a good deal on the shotgun version, tho.