4" components

I just bought an Audi and I have to get rid of the stereo in there. I would take the speakers out of my camaro but theyre 6.5" and front what I understand the Audi's are 4" upfront and 6.5" in the back. So my question is, can i mount the tweeters upfront and the woofers in back, or will that sound really messed up(I'm thinking it would) and the other question is what are some 4" speakers I should be looking at. I heard from someone that Boston are the easiest to install in an Audi because they ahve the same hole pattern but I dont think that would be hard to fix, anyways. I was looking at the Boston RC420's but havent gotten out to try and find a place to listen to them. Any ideas??
If you have any info at all on audi systems please let me know. Thanks

I would not separate the components. I would look into a set of coax and put a midbass driver in the place of the 6.5 As for what brand, I would go with what you think sound best