A friend of mine did exactly that - tap the threadless dropout - to run a Nuovo Record RD on a Gitane Tour de France. He did it circa 1974, and it was still going strong circa 2004 when he let a neighborhood kid have the bike. Of course, he also forced a Cinelli bar into a 3ttt stem (if you ask him how he did it, all he'll say is "It wasn't easy") so you be the judge of his wisdom.