Peachtree French door hardware
I'm not sure if our 82-400 can fit your door or not. You will need to carefully go over the dimensions we show for this handle set and see how they fit the space available on your door, especially the installation holes.
You mention you need to install these on double doors. I'm assuming the other side is a "dummy handle," which doesn't use any kind of internal lock mechanism. You may be able to install just the face plate and handles from our 82-400 set and keep the mortise lock aside as an emergency backup.
Ultimately, I think it may be worth contacting Peachtree directly to see if they still supply the hardware for your door. With the original handles missing entirely, there's no way to be 100% sure what will work.