There is no modification needed to the body (well there are a few holes and notches needed) to get the VQ in there. Because the Altima is FWD it makes the swap much easier than converting to RWD. I also believe the QR tranny and the VQ tranny are almost identical internally (much like the SR and KA tranny) the only thing to be swaped is the bellhousing. A few custom motor mounts and some wiring and you are all set 
Mike