Well it seems my opinion is in the minority, and I admit that I may be projecting anxiety based on the fact that my oldest and favourite ride in my modest two-and-a-half steed stable has had two heart transplants (that's bottom bracket shell removal and replacement, for the literal-minded). These two heart transplants took place in two different cities two hundred miles apart. The second heart transplant was to rectify the damage caused by the first one, as far as that was possible. Coincidentally, chances are that the fella that did that second transplant is the same fella that built one of the frames in your stable, Tonyf39, but I don't know for sure.
That was back when there was no market in 'obsolete' bike bits, at least not one I was aware of, and when I asked for that second heart transplant, I reasoned that it would be a good opportunity to get the rear ends spread a bit, not because I wanted to, but because I despaired of ever finding a half-decent 5-speed block again. My rear ends were at 120mm (or should have been--after that first botched heart transplant it is anybody's guess). I wouldn't dare ask for 130mm--I even felt bad asking for 126. In the end they got it to about 123mm, and I wasn't going to quibble about the rest....Neither am I going to force anything between those dropouts that doesn't want to go. 123mm....This is how the frame was returned to me from someone who's just done a first-class job of replacing my bracket shell. Does that mean anything? Maybe not, but it could be evidence that you should assess the advisability of the procedure on a case-by-case basis without assuming that because it worked on some other steel frame it will work on any steel frame.
So, that's my story... with all the sordid details of the first transplant left out. I am slightly wiser from the experience. Hopefully that fella who botched the first transplant is now a more diligent frame repairer than he was back then. always in the back of my mind is the thought of my bracket which has been heated up to brazing temperature at least four times, probably six, and like I said, perhaps I project that anxiety onto situations where it is unnecessary.
But seriously, anybody, have a look at the picture of this Harris frame on the other thread, where you can see that there is no paint around the chainstay bridge, and possibly hasn't been for decades, and tell me you'd be happy to advise someone to yank those stays out to 130mm without even seeing the frame first-hand?
I'm very far from being an expert. And I'm not saying anyone is wrong. I am just advising caution. Maybe I'm just too cautious and you can pull those stays out to 145mm with a clear conscience. I would genuinely like to know...maybe the OP also would... What is the acceptable limit for this procedure? On old and possibly corroded 531? Alternatively perhaps those rear ends are already at 130mm- nobody knows except the OP!