The fog lights that are stock are some ludicrous cheap nonsense; they connect with one white wire (positive) that comes from the harness and a black one, that terminates in the headlight shell. The lamp itself grounds via the shell as well. You have to cut those cables as near to the ends as possible and figure out some other way to wire them up. I just put two Posilocks there which is super easy, reliable and reversible.
The fog lights will fit the shell just fine, I've seen Rocket T's with those on them (at least in pictures). It's an easy job - open the headlight shells and find a soft surface to rest the ring/reflector on with the glass down, pry off the clips that hold the reflectors to the trim ring, put the new reflectors into place and replace the clips. Then just mount the trim rings again.
The Truck-lite main 7 incher will stick out a bit as the glass portion is thicker than the stock. I've seen Harley riders getting frenched trim rings to avoid that.