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hoping for your advice
Depends how much you value the frame vs. how much you value being to use practical hubs in it for riding. Springing it open will bring forward the time when the weld at the inside of the chainstay/BB shell junction cracks. If you don't mind that you're going to be using up the frame, go for it. Riding it for a few years is probably going to be more fun than hanging it on the wall of your man cave for a few decades unless it's something very special.
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when the weld at the inside of the chainstay bridge cracks
FTFY
Is this also true for crude Al frames from the dark ages?
Can't think of any 126mm Al frame other than an early Klein, Cannondale or a bonded Vitus type affair.
My touring 'dale was factory built with a 130 hub in a 135 spaced frame. Might have been an oversight, but the deformation seems well within the elastic range and the frame is still fine after >25 years.
Kinda hoping for your advice.... 😁