Hybrid Audio Imagine are a great $200 convertible component set that sound good with litte power. Very efficient. Would make a nice drop-in replacement. 6.5 in front doors, tweeters in new locations using supplied mounting hardware, and 6x9 in rear for more bass response.
If you plan on adding a sub later, you can put 6.5 in rear.
I61–2 front
I69-2 rear
Or you could just drop I69-2 in front and rear. But the 6.5's have smoother midrange response.