Generally 50's woodrails inserts sink as opposed to being cupped.
And usually from this era they do come out with hair dryer and gentle pressure from underneath.
Then a small bit of wood glue and to level and job done.
And put an object on top of insert while it dries as they can rise slightly on drying.
Don't recommend epoxy as if you make an error it can look awful.
The enemy of good is better!