You have 4X6" in the front and 6.75" in the rear.
A lot of folks, including myself took some plywood or MDF and made an adaptor to fit 6.5" or 6.75" speakers up front under the door panel. Also, a lot of folks would add a tweeter on top of the doors near the dash vents. That make a huge difference in the highs.
For the rears, I installed same size 6.75" Kenwoods. Fit well, but would like the punch of 6X9s muself.