300 WinMag burns a lot more powder than the '06 and for comparatively little actual improvement. What shape is your 1917 in right now? If it still is restorable, then this would be a crime against humanity or something.
That said, the bolt face can be opened up to accept the larger rim; after that it is a straight rechambering job but the feed rails may need to be opened up for the fatter casing. Call it a couple hundred minimum.
300 WinMag is same length as the '06, so, if your throat is at all worn, you gain nothing: a bad throat is still a bad throat.
MORE sense to rechambering a slightly-worn P-'14 and handloading the 300 WinMag case with .312" slugs: bolt is already the right face, so it is a straight rechamber-and-feed-rails job, call it 150 or so. Good part is that it will clean up most bad throats at the same time. Need to replace the Magazine Box at the same time, use 1917 box.
Just my 2 nickels' worth (since we Free Canadians are no longer allowed to use pennies).
"Everyone should have a Magnum rifle; you can miss your target just SO much faster!" C. Ens, Gunsmith