You got me wondering about this. I have a extra R-14 and took the screw out to see what it is. I found it was a 6-48 headless straight slot screw. It is .235 inches long and has been ground to a very sharp point on the end. It was buled to match the side of the sight. If no one modified your sight, you could make a screw to fit. The other thing I not certain about is if the R-14 sight has the same screws as your sight for the model 8. Removing the screw on the good side and seeing if it is a 6-48 will tell the story.
shot1too RSA