These are axles from an armoured series lightweight Landrover. Most likely from the Northern Ireland conflict. But shows how the addition of channel can greatly strengthen an axle. Just some square channel cut to fit the profile and welded along the existing tube.
Front axle, at an angle to the ground:
Rear axle, straight to the ground.
I'd seam weld the whole thing to prevent dirt getting in there, or leave holes so it could be washed out.
And, a tip I was given by a freuhauff trailer engineer, when writing cracks, weld a brace across, not inline, the crack, the stress that caused the fracture is not going to crack the brace.