Thanks, bsa, those pics really help. Here are pics of mine, for comparison:
Mine's a post-'64 (circa '71) .338 Win Mag, and comparing the two in the photos clarifies that both the forward and rear bridges in yours have been hogged out (?) to accommodate the extra-length H&H rounds... compared to mine, where the top metal runs straight across (athwartships, so to speak, or due east and west maybe) both fore and aft. Well, maybe not as obvious as it would be if I didn't have the mount bases installed, especially the forward base that extends over the back of the forward bridge a bit.
Sorry, all, that I didn't post more info at first. My questions came about as I was progressing through a "swap all the scopes" project on a few rifles at the same time. Mostly just passing time, but it got me gloss scopes on gloss rifles, matte scopes on matte rifles, size/weight/magnification slightly more appropriate to platform, cartridge, expected use, etc...
So here I am, reviewing various rings and mount bases... and I'm reminded there's a difference in hole spacing for the rear bridge mounts. Hmmm... Whyzat? Just as a matter of interest, mostly...
I've "known" sorta-kinda all along that the "long" Model 70s could handle both .30-'06 length and H&H length cartridges... but without having one of each to compare... and without seeing really good pics... and with measurements indicating an H&H cartridge could actually fit in mine (although without knowing whether it would "work" or not)... it just wasn't obvious to me how Winchester solved all that. Very clear, now, and I appreciate the education.
-Chris