You have to use stock parts or their aftermarket identical equivalents.

What makes the new hub stronger and more durable the the stock one? That -- whatever it is - is what makes this illegal.

I saw a rear hub break on a 325 in a 100 mph corner at Roebling. Bad accident. Certainly want to avoid that, but the way we have to do it in IT is to simply replace hubs on a frequent basis if they are a known weak oint.
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I would argue based on the piston interpretation that a billet hub that was dimensionally identical would be fully legal in IT.