Can't claim to be an expert. But a data point.
Back in the early 70's I, kind of, tried this conversion on a 1971(ish) International. The crank was a Sugino Mity Tour 34-42-52 if I remember correctly. The Round-Oval-Round chain stays didn't allow a very good chain line And the deraillers of the day, Suntour GT (of some flavor) and Shimano long cage (Deore? probably too early?) didn't really work very well with the short chain stays. I ended up going back to the original Campy deraillers and a 28T large cog on the freewheel and the Campy NR Double 52-43
I know there are a ton of modern bikes with triples in front and short chainstays, but with the existing stuff back then, I could not make it work well enough for me to use.
I guess my point is, this might work if you use modern cranks, deraillers, chains and the other stuff, but using vintage stuff the performance is not going to be great.
AND as usual, YMMV
later
Brad Luecke
Columbia Missouri, USA