Well not the end of the world if you go for the milled type, they are usually more expensive though.
I had one, but I gave it to the last guy trying to do a trench gun.
The rear sling mount should be the stamped type. The Thompson, the 1903, The krag, and the trench guns all shared the same rear sling swivel. But searching for the 1903 one will net you a lot more results.
If your but stock isn't already recessed for it, it will involve a bit of woodworking to...