Offroad armoury used to sell axle trusses, I would presume they still do???
My new axles I bought off tim pink are sleeved with 3" red band tube, think its got a 6mm wall then uses pipe caps for diff guards, here's one of his pics when he first did them, ill get a few pics next time I'm at the workshop.
One thing to note though, when you truss a suzuki axle I would take it very very slow! It's very easy to warp a suzuki axle welding it, literally just tack it on, let it cool, weld a tiny bit, go for a cuppa, weld a tiny bit more, leave it to cool, weld a tiny bit more, have a cig, weld a tiny bit more, have some lunch, weld a tiny bit more, have a cuppa etc.
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and don't run any long beads of weld, just and inch or so at a time.