Here is a link to the "classic skimmers" by reef octopus (offsite) -
http://reefoctopus.com/product/octo-classic-protein-skimmers/ . Under the Technical data you should be able to find the modern day equivalent and it would be reasonable to assume that your older skimmer has similar specs.
Even after all that, make sure the skimmer is large enough. Generally you want a skimmer rated for a tank about double the size of the tank you plan to use it on. In other words for a 110 gal tank, you want a skimmer rated for about a 220 gal tank.
Check out the condition of the skimmer carefully, especially the glued joints and the pump parts. It's amazing how much wear and tear a skimmer can get after years of use.
