+1 on the 753 heat treated tubing being resistant to cold setting .IIRC, the heat treatment basically causes the frame tubes to act like a springs, so cold setting cannot be done. but it does not mean you cannot squeeze in a 130mm spaced hub in there, as the 4mm difference isn't really that much. Only thing one might be concerned with is that you will be putting the rear triangle tubes into a state of constant built in stress when the wheel is in and the skewer tightened. Is it enough to eventually affect the integrity of the frame tubes or the brazing connections to the lugs over time?....I dunno.... Maybe an engineer with more knowledge and exeprience with materials knowledge and finite element structural analysis can chime in......
Just wondering, what is the damage on the chainstay you mentioned that neccesitates having to change it? I can't really see it in the pics.

Chombi