I just finished swapping in some seats for an '06 grand prix and it did require some fabrication. first off the nuts on the bottom of the donor seats were tack welded in 3 spots on each nut with a tig. i was unable to cut those free and the impact wrench only broke the weld on the stud, so they spun. i ended up cutting off all the brackets and studs flush. this allowed me to weld some new 5/16" bolts onto the bottom and mount up the yj brackets. since the old bolts on the donor seats held some of the reinforcing plates in place, i had to carefully weld them to the thin sheet metal near the front of the seat and on the 1/8" at the rear. this is best done while the studs are still holding everything together.
also, cutting some of the fabric off the rear of the seat will allow room for the tracks to move back when you slid the seat back for the long legged folks. it's easier done before you install them in the vehicle.
The seats off more lumbar and side support than the factory seats. the side support is really ideal and the lumbar is just a nice step up.
In hindsight, i would have moved the seats 1" to the outside to allow for the wider console. the seat belt on the gets caught between the seat and console every time you lift the seat forward. it is not easy to get it back to a usable position.
if you leave the plastic trim on the sides of the new seats, you'll need to trim the passenger side to allow for the seat lift handle to operate. it's quick and easy to do so with any cutting tool.
Tip: Don't forget to cover your seats while welding and grinding. I thought having them upside down would be just fine but sparks still found their way to places i'd rather not have melted. And keep some water handy for the foam when it catches fire.
this pic is of the seat while still installing. it is dirty but bolted up to the frame and set into it's spot.