I like it. It shouldn't be hard at all to make it feed from the mag. I wish I would've goten some of those barrels with the front receiver stubs attached. You'll enjoy magnum stuff with a short barrel and a brake, i've got a Savage that I rebarreled to 338 Edge with a 17.75" barrel and a brake. It's pretty spectacular.
I've thought for years that a cut down 416 rigby case necked to .311 and loaded to sane working pressures would be cool, the rigby case head should match the x54. Only problem is the high cost of brass, for that matter the 338 Lapua brass casehead should fit as well, but that brass is expensive too.
Get you some O1 drill rod and make a reamer, I've got the reamer specs here if you're interested.