If the guitar is at a local guitar store, you can find out pretty easily. Tap on the pickguard in between the pups and work your way towards the outter edge of the body. If it sounds hollow and then becomes dense, it will fit humbuckers. This routing job is also called a swimming pool. I believe it was in the 80's and 90's that they did this because it cut down on production costs, but also messed with the tone. The word on the street from Fender is that they have discontinued this practice and only do routing for single coils on their recent Strats (last couple of years). However, I'm not sure whether or not American Strats were routed like above.
