Dating old furniture
There are also companies that sell retrofit hardware that will fit the 2-1/8" hole.
They provide everything but the doorknobs themselves.
A bit key mortise lock has a striker (look at a modern door - the thing that goes in and out) that holds the door when you close it and a deadbolt that is thrown with a skeleton key.
A mortise latch does not have a locking function and is much smaller and easier to install.
If it has the large hole from modern locksets, see above for filling the hole.
With cast iron or black antique hardware I suggest a dab of black paint on the screw heads for a more pleasing appearance. Brass & bronze are soft metals that are easily scratched and cast iron has no flex and will snap just like a piece of glass.