..........power expectations........

Well those pollution era 360s were factory rated at 240hpNet, and Supposedly never even made that. Whereas even the 318 Magnums were rated, Net, at 230, and did make the numbers. I imagine the Magnum 360 would be quite an improvement. By direct inference the 360Magnum should be a minimum of 260Net. But if it is a 300 crank hp crate, the equivalent net hp might be a little more
But the really nice thing about the Magnums is the abundance of low speed torque, and they have loads more potential.I wouldn't hesitate for a moment to make the swap. Just be sure to correctly mothball that low-mileage LA. Someday you might be wanting to sell that Duster, or pass it on to a family member, and then a numbers matching engine will be worth something.