Depends on the speakers- My 6x9's and 6.5's both dropped right in. Had to rig the tweeters though. What are you planning to install? If it's a popular brand some members may be able to tell you if they'll fit.
All 6x9's should just drop it with no problem for the back. The fronts may or may not. If they don't you can try what I am currently doing. I am taking the plasitc housing off of the factory speakers and sitting my new aftermarket speakers into that so it will just bolt back in. In order for the speaker to stay in the housing I took some clips, cut them in half and made a lip on them and am going to use them like a washer to hold the speaker in there. I couldn't find any adapters around here so I doing it that way.