I want to use the Leupold Dual Dovetail 2-pc bases. I bought a set for a M70 Winchester but the rear part of the base doesn't fit. The spacing on the screw holes is much shorter on the Safari Express than this base that I bought (apparently what I got is for a 'standard' M70).

There must be a special base, specifically for the Safari Express?

The rear base hole spacing on the Safari Express is .330" The Leupold number for the matte blue bases is #54240.

You need the set identified for the H&H magnums - post 1964.