Spindles, hubs, kingpins, bearings, and brakes are much larger on the big rigs. It's highly unlikely they would have used the same axle forging to span that range of weight capacities. "Sid's Axles" seems to be the current guru on straight axle information. You might try contacting them if one of the professional part number crunchers on this site can't give you some guidance.

I grew up around a shop in Nashville in the 1950's where they did wheel alignment by bending straight axles, so unless your axle is bent into a veritable horseshoe shape, a couple of 30-ton jacks, some big chains, and an I-beam can probably straighten the one you've got. I'd suggest contacting a shop where they do wheel alignment on 18-wheelers.
Jerry

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