Buckstix,
I have a copy of the Big Bore Rifles by Jack Lott - far worse condition than that shown but is in .pdf form.
Some of the photos shown in your initial post are there in it & as Wanabebwana said the grain on the stock matches so I reckon you have the original .458.
Shame about the original papers!
Great find mate, but boy she'd kick at 9lbs!
93x64mm