I would use a M70 Winchester Long action with magnum bolt face, or the Montana MRC M99 Long Action with magnum bolt face. Either would allow the cartridge to function with a minimum of alteration. Using a Mauser involves a good bit of machining and new bottom metal.

Although the design length of of the 400 H&H is 3.500 inches, a 3.600" magazine (M70) or a 3.65" magazine (MRC M99) lets you use the longer monometal bulets without seating deep and wasting powder capacity.

A No. 6 contour barrel, 24 inches long, and a walnut stock will put you into about 9-1/2 pounds rifle weight, without scope or mounts.

Put a recoil lug on the barrel, install a NECG Masterpiece front ramp with blade & hood, install a NECG Masterpiece adjustable rear sight, or a NECG Multi-blade island type rear sight, add a barrel band type front swivel lug, and you will have a nice classic rifle.

Be sure to design in enough cast off, drop at comb & heel, and pitch of butt in the stock for use of the iron sights. Install two cross bolts in the stock, and bed properly with high strength bedding compound. I also install a 6 inch long 4140 heat treated rod in the wrist of the stock to prevent failure or splitting. Also need stainless steel pillars in the stock to prevent crushing the wood.

If you want to scope the rifle, use Talley detachable mounts and a mid power scope, such as a 2-7X or a 1.5-5X Leupold.