6.5 v. 6.75 Polk Speakers

I have a 98 Mitsubish Eclipse with the infinity system (or did before I changed headunits).  I am going to be replacing the old speakers in the doors and dash with either the Polk db6500 or db6750   6.5 versus 6.75 component systems

I wanted to replace the stock doors with the 6.75 however the stocks may be 6.5.  Crutchfield says that the 6.75 will fit in the door (somehow).  I also talked to one of their reps, and he said that the actual speaker size between a 6.5 and a 6.75 is the same, and the baskets are just different, I dont think this can be correct.  I want the 6.75 for more bass, but if it wont fit there is no point.  Also, anyone know where I can find a bracket for the tweeters?  If not ill just have them pro-installed and let them figure it out.

Thank you