I am riding a Trek 6500 dating 2001-2002. The dealer at that said the bike was adapted for using disc brakes. Now I'm looking to mount disc brakes and I am able to spot the international mounting structure on the RockShox Fork. I didn't see however an International mount structure for the rear caliper. The only thing I can spot are two small holes in the lying rear fork. Is this the place to mount the rear caliper and if yes, which kind of adapter do I need?

Frederik