It seems to me that the 300 winmag is so close to be ready for gameday already that I would not be in any hurry to do much other than change the stock.
Then work up a load and see if you have a solid long range keeper.
If the 7mm is a shooter, then sell it to get a nice foundation for the winmag.
I would pull the PST off of it and sell it separate.
That's the best I can hypothesize on saving you cash. But there is no end to how I can tell you to spend money
Although Ity looks like one of them triangularized barrels which I loath. So a new barrel and blueprinted action would be required in my stable.