Hi, 2 cents from me
One possible solution would be to find a modern smith who still practices casting techniques that are the same as those used in the past. There are a number of people, such as Tod’s Workshop (see YouTube), who are into making weapons and armour the old way, and then stress-testing it. They might have some advice on how to replicate cast pieces, or be able to create one for you. If the form is not important, then just get a piece for experimentation.
Now you have a modern piece sanded down you could compare that with the one from the older practice to see if there are significant differences.
On a related note: You could get a modern cast tsuba and see if you could sand it to make it appear closer to a genuine Edot one…