Look for 6.5s that come with the 6x8 adapter plates, or roll your own adapter plate. I hate to say it but most 6x8s ****! I've tried just about every brand because I have owned Ford vehicles off and on since 1996 and I have yet to hear a 6x8 that I like.
If I absolutely had to use 6x8s, I would give the Image Dynamics component set a try. Of course, that would blow your budget!