Easier if you start with a P-17 action and a P-14 bolt. P-14 bolt is correct for the base of the 7 Mag round, P-17 action has straight feed rails already; just get them cleaned out.
The internal magazine on these rifles is a simple box, easy and quick to change out. If you are starting with a P-14, likely you will have to remove internal wood to get the longer mag box to fit properly; the rifles were designed for the shorter box of the .303 round, although the original design was for a magnum-class 7mm round, the .276 Enfield.
No problems with a barrel; it is a standard thread, no tricks to cutting it: not at ALL like that miserable left-hand, 3-to-the-inch, half-buttress thread in the 1905 Ross!!!
This is a relatively common conversion, although definitely NOT to be undertaken if you have an original rifle. You could be haunted forever if you wrecked an original rifle to do this. Lots of them already around, already wrecked.
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