5x8 oval, but I have made some templates that put my 6.5" speakers in the place.
My suggestion is stay away from oval speakers if at all possible. They do not sound as good as round speakers do. Also the tweeter location is still a good option to mount your tweeters in if you go with a set of component speakers. If you do decide to go with 5x8's, then I would suggest to run JL's component set. Put the midwoofer in the stock location and the tweet where the stock tweets used to be. You can mount them with some back strapping if you care to , or just glue them there.