I'd start by taking the front bumper off of the 6 and see how the 3 bumper sits. Beings that you're not new to cars, you could also take the 2 bumpers to make 1 if you know how to plastic weld. This is an art that I think all diyers should learn. With the correct sticks or even extra bumper pieces that won't be used it will make a great bond between the 2.
I've seen similar ideas like this come to life. If anything, you could take the top half of the 6 bumper and mold however much of the 3 bumper that you want to it. I want to say that I had seen someone doing this in the DSM world where they took an EVO front bumper and molded it to their 2nd gen Eclipse. I'll try to dig up that thread because it was cool to see it getting done. Now I don't remember if I saw it all done or not because about the same time I got rid of my Eclipse in favor for my 6 so..
As far as the fogs, I'd have to see the fogs and what the bumper looks like (mine is a 03 so nowhere near the same lol). Push come to shove you could heat set some mounting brackets into the bumper to give a starting point for them to bolt to.
I'm still working on mounting Ford Fusion fog lights to my car and this is what I came up with to bolt everything to the car once I make the fog to bumper brackets. I heated the L brackets until they were almost red and then carefully melted the bumper just enough for the bracket to slide about midway in and then used more melted plastic to cover the metal. Once it was cooled, the metal had bonded with the bumper and is very solid.
