Adding Locks to Antique French Door
Those types of latches for had specific shapes to follow the door edge profiles. You may be able to find a new latch that will work, but I would suggest shopping for an antique latchset that will suit your needs and have it reconditioned by a locksmith.
After that is accomplished, then cut out what is needed to get the new or reconditioned latchset to work. Don't just remove what was filled in, although it may be needed anyway, but some filler may be able to remain, since the new lock may have different cutouts needed. Then again, in making the new mortices (cutouts) the filler may fall out anyway. Just as well, if it does, it can be reset properly and more permanently.