Hi Marplot-

While all pre-64 Model 70 receivers are the same overall length, the factory hole spacing on the bridge differs between receivers accommodating standard cartridges (30-06 length or shorter) and H&H Magnum length cartridges.  This is because the bridge was partially cut away to facilitate loading of the longer than standard H&H cartridges. 

Look at this photo showing an H&H receiver on the left and a standard receiver on the right. The two holes in the receiver ring, and the rearmost hole in the bridge are in about the same place in both, but the forward hole in the bridge is in a different location.  On the standard receiver, the two holes on the bridge are 0.865″ apart and the distance between the rearmost hole on the receiver and forward hole on the bridge is 3.800″.  On the H&H receiver the bridge holes are 0.425″ apart and the distance between the rearmost hole on the receiver and foremost hole on the bridge is 4.250″.

The second photo compares a Redfield 70A base (bottom), which fits the standard pre-64 action, and a 70AM base (top), which fits the pre-64 H&H action.  Obviously these bases only use three of the four holes and the 70A base doesn’t reach the forward hole in the H&H bridge.

I am not familiar with using modern “rails” on Model 70s, but I think most manufacturers use the term “long” action to distinguish the Model 70 standard length action from the later post-63 “short” action, i.e. receivers that are actually shorter in OAL, e.g. made specifically for 243/308 Win length cartridges.  So unless the “long” action rail you’re looking at was made specifically for the pre-64 H&H receiver it might come up short on the bridge.

As for ring height, I do not know.  I have never put anything larger than a 40mm objective scope on a Model 70, and they generally work with medium height rings.

Hope this helps,

Lou