Was looking at some stuff and came across this. It is supposed to be bottom metal for a Pre War Mod 70 in .300 Win. The spacing compared to a Williams piece seems correct, but neither an original Winchester long box, nor the Willims standard box fits in it.

Out of curiosity when one opens up a standard Mod 70 to rechamber to a 7mm Rem and .300 Win is it SOP to open up both the bolt face and the front of the receiver or is the receiver an "option?"

The reason I ask is that the 2 Pre War receivers in the pics are both "standard" (but with the bolts opened)configuration when compared to the "long" H&H receiver.

A wild guess here, but many years ago (at least 30) there was a company called London Guns that sold a drop box casting complete with integral magazine box for 375 H&H length cartridges. There were no holes drilled so as to be able to use it in any action you wanted without worrying about spacing since you drilled the holes yourself. I built my first 416 Rigby using this set up, but did have a gunsmith machine off the integral box magazine since it wasn't long enough and fabricate a new one.
This one in you photos look very similar to design and that fact that the original was a somewhat rough casting, hence the polishing/filing marks on yours.
Could be totally wrong, but thought I would put it out there.

Ooo,Ooo,Ooo, I Know, I know,

IT'S bottom metal

Sorry I had to. N

No clue as to the application though