VC
You won't go wrong with either cartridge!
I have a Parker Hale 1200 rebarrelled to .308NM, nominal barrel length being 26". Any large Mauser action or similar will suffice.
Looking at loading data they are more efficient than the .300WM, but in all honesty there is nothing between them! The original factory short .30 magnum, the .308NM predates the now more readily available Winny mag. Its a shame really, its a fantastic cartridge, all down to marketing really!

I've only used 180gn & 178gn A-Max Hornady projectiles, all shoot to the same POI at 100m.
A note to all here, I have had my throat lengthened so my loads are over listed maximum.
76gn of AR2213SC for either projectile, getting 3020 & 3070fps respectively, Federal 215 primers & loaded to 85.4mm OAL which just fits inside my magazine.
Yes the Norma brass is outstanding, I've lost track on the reloads they've done with them, they get an annealing every so often, no more split necks now.
The A-Max being slightly more accurate - 3 shots going into 23mm.
So start at least 5% down from there & work up.

AR2209 doesn't work at all in my rifle at all, the groups were horrendous!
Norma 180gn yellow tipped ammo clock 3060fps in my rifle & consistently do 25mm 3 shots groups.
I have an old Outdoors magazine somewhere at home, dated in the 1960's, Parker Hale did bring them out then on Mauser actions - hence why I went the way I did!
Best of luck with the build, it can be a bit finnicky to load for as is any cartridge at times, slower powders are far better anyway.