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There is zero science in there.
Having seen first hand Vitus bikes with bonded tubes that have popped tubes while being ran fixed, I just provided @JoeGW with some unsolicited advice.
I am sure you have the actual software to show the areas of the BB / chainstay that are under load when you do a mad skid!!!
Since it is a family heirloom, I image he'd prefer to keep it in one rideable piece as long as possible.
I can't remember if the lugs are bonded or welded on these old aluminium Peugeot but regardless, it will 100% explode if you ride it fixed as the BB cluster has not been designed for it.
Just turn it into a nice singlespeed with a chain tensioner and enjoy it