I also have a 721 in 300 H&H. I bought an old factory BDL stock off of ebay for it. You do have to make room for the safety as its a little different, but the straight bolt handle should work fine. You also have to make room for the barrel bulge of the rear sight. This is what I've read on other forums, I havent gotten around to doing it yet. Plus you'll need a BDL trigger guard assembly or get the ADL stock and cut out for the 721 trigger guard and plate. Or make it a blind magazine with an ADL trigger guard and magazine box.
The stock was originally from a magnum chambered rifle so the barrel groove is close to the right contour but I won't know for sure until I find time to actually fit it and I still have to buy the BDL trigger guard and floorplate assembly.