I'd thought that right side notch was for the rolled projection on the magazine cuttoff, as-is/was the slot on the right side of the action with the lowered wood. It appears to me this forewood was originally a military piece of wood off a LeeSpeed with a magazine cuttoff.

Bear with me, as I'm certainly not any sort of an authority on these rifles, nor do I have more than a working knowledge about them. This is just a guess as to the nature of the reduced height of the ejection port area wood and the notch on my part. I thumb notch would be rounded, if it had one, not angular and square.

The screws appear to be poor plugs for holes drilled and tapped for the front 2 holes for a el-cheapo Enfield scope base.