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4.5mm either side should be fine, but there are a couple of things to consider.
You'll need to brace the chainstays just beyond where the chainring extends, to maintain clearance.
I'd also brace the frame at the seatstay bridge, so that doesn't get stressed.
You'll need to tweak the dropouts, after setting the stays, to get them parallel again.
Using something to screw the stays apart won't work, unless both the tool and the frame are fixed: otherwise only the weaker stay will move.
Should I just make life easy and fine a 130 wheel?
There is that...
135 hub in a 126 steel frame, yay or nay?
Was thinking of using DIY headset press in reverse to cold set...
Should I just make life easy and fine a 130 wheel?