Upgrading an old steel bike...

alfeng

Brown had some (not many, but glaring if you noticed them) errors; but, I think you mis-read Sheldon Brown's comments regarding top tube length on lugged frames ... or, maybe he didn't state it clearly.

It wasn't that one-size-fits-all would do for all frames, but that was the consequence of mass production BECAUSE the various lugs are cast at certain angles.

So, while various angles were available -- e.g., 72º, 73º, 74º -- for the head & seat tubes + BB shells, they have fixed angles UNLESS the framebuilder forges/hammers them to a new angle. Consequently, for off-the-shelf bikes, standardizing the bazillion lugs & BB shells for 72º or 73º frames were most easily accommodated by simply providing a different stem length.

TIG welding changed frame design AND rider frame fit -- miter the tubes as needed (i.e., ANY angle), then weld.

A vintage 52cm (c-c) frame would probably come with a 7cm stem whereas a current 52cm (c-c) frame might have a 12cm stem ... almost a two inch difference because the top tube on the contemporary frame will undoubtedly have a shorter top tube & some notions on frame fit have changed over the years (i.e., touring vs. "racing").

So, the same top tube length on vintage steel frames really wasn't a one-size-fits-all will do situation but the necessary result of mass production.

alfeng

FWIW. I think that INDEXED SHIFTING is improved if the rear derailleur hanger is re-aligned after the stays are spread ...

On SOME frames, the dropouts may actually be slightly boat-tailed (well that was the case with my FUJI S-12S LTD, for example) ... the dropouts & rear derailleur hanger on the particular frame became parallel to the center plane of the frame after I spread the stays from 126mm to 130mm!