I sure hope it shoots the 174s well enough but I think at the time the 215gr load was all that was available.
It’s simply stamped “303 Nitro Proved”

As I understand it, the screws on either side hold the ejector rods in place and the one on the right does double duty also holding the flat spring in place.
The flat spring on the right has a tooth that holds the ejector back until the ejector force overcomes this spring and pushes past the tooth giving the ejector a more snappy action.