I've never seen Seyfried's .416. Marrakai, are you saying the gun had an open notch mounted roughly about on the receiver? That's where it looks to me such a sight would have to be mounted if it was to approximate the distance of the sight on Peter's gun. not saying it couldn't be mounted thusly, but I've never seen such placement of a notch rear sight on any gun.

Peter, I suspect you will recut a dovetail further out toward the front sights with your new rear sight?