Craig Griffith, who did the aforementioned Swiss bicycles website, was very helpful to me as I tracked down information on my c.1974 Allegro. I trawled the net seeking info, because mine does not conform completely to normal standards for these bikes, at least as known in the examples that were imported into the U.S., but his information was a good point of departure for me.

For really old Allegros, I would say start here and then look at this one and this one and most especially at this one, which makes my little heart go pitter-pat.

I spent a lot of time studying this one at the Steel Vintage Bikes site.

This gentleman's adventures in restoring his Allegro is a good site; also, this one.

From obsessively studying Allegros all over the 'net (there are many more out there), it seems to me that by the early 60s, if not earlier, they used both Nervex Professional and Bocama model 14 pattern II lugs in both chromed and painted finishes, usually with with Vagner PL flat-topped crowns. The 531-tubed Allegros, anyway, used Campagnolo ends and came stock with the same driveside chainstay cable stops; brazed on fittings for rear brake cable stops and housing stops for use with bar-end shifters appear on machines built over a wide time span too, which makes me think those touches were tied to specific models.