Wow, an antique. I very vaguely remember the Ghisallo brand; its from back in the heyday of Jeunet, Gitane, Peugeot, and a slew of other French brands. At least, I think there was a Ghisallo brand. Thats a very common name in the biking world. The Madonna del Ghisallo is the patron saint of bicyclists, so today you see the name on bike models, helmets, and more.
Anyway, its a safe bet this is one of the avalanche of French bikes that poured into the United States during the 1970s. Whether you have something valuable is difficult to say. A lot of the bikes that came in back then were, well, cheapmade with fairly low-grade steel and inexpensive components. But, if your bike has Campagnolo running gear, Excell or Vitus tubing, Mafac brakes, and maybe an Ideale saddle, then perhaps you have something. Labels should all be readily visible.
Regardless, an old steel bike can be rife with problems. If the stem is original, then give it a very close look; they can crack and fail catastrophically. If would be nice if your local shop could get the bottom bracket offit almost certainly needs fresh ball bearings and greaseand peer inside the frame to check for rust. Give the frame itself a careful look for cracks or weak points caused by rust. French paint and chroming was notoriously bad back then.
That said, if your bike is in good shape has a decent pedigree, then you should be in for a treat. Bikes of that era handle and ride very differently from modern bikes, and many people believe they were smoother-riding with more forgiving handling.
So, get out there and ride your new/old velo.