You should be just fine with the 1:10 .308. I've used reduced loads with light bullets in .308 down to "around" 2200 fps, in 1:10, and they shoot well. Seems like Remington 721's, 700's and the pre-64 70's used a 1-12 twist, if you think that the slower twist is an advantage.
I'm pulling the barrel off a Vanguard chambered to .300 Weatherby to make a .300 H&H on the action. (I have NO use for the Weatherby cartridges, and have more than a thousand new H&H cases) I suspect that those various .300 whatever Mag barrels came off for projects, especially back when everyone HAD to have a 416 of some flavor.
Another excellent source of 30 caliber barrels are take-off 1903 and A3 barrels, and generally, can be had for a song if they've been cut back. New-old-stock, in the wrap GI barrels are pushing $250 these days, but sportered barrels go for dirt.
Nice to see someone else considering the "pre-AAC Blackout" .30 caliber round!