I would get the Moser 31-spline 'race' axles.
Plenty strong and durable for a 12-second car and even that (eventual) 10-second machine.
The Auburn diffs seem to generate a mixed bag of opinions; some love 'em, some say they rot. I think you could just as well get the stock (Traction-Lok) differential beefed up and use that successfully for now. Cheaper; and rebuildable.
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