Sorry mate, I dont like what I see.
Looks like someone stuck an SLX sticker on the frame.
Paganini frames that were SL or SLX had engravings (pantograph's) all over the lugs etc.
They also had Chrome forks and rear stays. Dropouts were either Ultech, Columbus or Campagnolo.
Bottom bracket shell was Cinelli.
Yours is most likely Columbus Aelle tubing. Maybe, just maybe might be Columbus S if that S stamped on the BB relates to that.
They usually have the tubing type stamped on the original fork steerer.
The internal cable routing is typical Paganini style, so its safe to say it is an actual Paganini, just not SL or SLX tubing.
Judging by the rear caliper bracket design, it is an early Pag frame, probably pre 85/86.
Sandblast it and repaint it. Should be nice.
Thanks Cooker... rather the conclusion I was coming to as well! Also interesting to note that BB is English thread rather than Italian, which (if really Italian made Columbus frame) then is apparently indicative of stuff from Belgian shops like Plum-Vanqueur, who I understand sold the Paganini bikes.
Any ideas regarding as to how to work out whether frame is from Columbus Aelle, rather than something else altogether?
Spacing on rear dropouts is 126, which seems to support your thoughts regarding age.