there are two variations of these stocks that will work, one with the shorter reinforcing blocks front and rear, and the heavier one with the full bedding block.
here is a snip from Stocky's
"If you don't want to open channels on a standard BDL conversion or own any magnum-chambered 700, choose the 2265 Alaskan Ti for lightest weight, the 2461 Alaskan II for a slightly heavier stock with the full aluminum block. Either are built for the heaviest magnum recoil. Short mags use the short action version of either Alaskan stock for a drop-in fit."
i have both of these and they both will indeed stand up to the .375 Ultra recoil.
here is the 2265 on my SPS .375 Ultra