The pin you see in the picture locates the fore end in correct relationship to the plate screwed to the front of the stock below the front edge of the receiver ring. I have never seen one where the pin retracts. The Fraser fore end is completely removed from the rifle, before the barrel is unscrewed.

The locating screw in the side of the receiver ring, I believe, is original to the rifle. Every one I have examined has one, and they are all of a similar appearance.