if you can get a 7-speed rear in there without pulling the dropouts apart, then it's been spread (cold-set) to 126 spacing from what would have been the original 120.
I think any Campy gear would be perfectly suited on an Allegro, but maybe some Weinmann brakes to keep a little of the Swiss on it.
I have a few left-over decals from my re-spray, nothing like a complete set but they were printed from my own artwork so I can vouch that they were a very good match to mid-'70s originals...and I'll make you a deal
Here's a shot of my serial number (before re-spray)