While you can probably get away with installing the Kerker slip-ons by alone, to get the best possible throttle response and engine performance, it's always best to get some sort of fueling modification device. You don't need to bother with an air filter or anything, but it wouldn't hurt to add one since you're already improving the exhaust, too. Basically, any time you change the way air gets into or out of, the motor, you'll want to adjust fueling appropriately to maximize any performance gains available from the new setup.
To do this, we recommend either, a Vance & Hines Fuelpak FP3 or a Dynojet carburetor jet kit if your bike is carbureted.