If you look at the picture of the belly pan from the U12 Bluebird (same as our Stanza) SSS-R the tunnel is bigger for the drive shaft and the carrier bearing. Also it has the kick out for the cat in the middle of the picture. It would be a large amount of money and time to convert a USDM U13 into an AWD Bluebird SSS ATESSA.
I would recommend doing an SR20DET swap from a U13 Bluebird and then using the P10 G20 or B13 SE-R trans and hybrid axles to fit the Altima. Also you could do a turbo kit on the KA24DE and have a 220hp reliable driver. Turbonetics has a kit and Jim Wolf could put together something for you as well. If you want an SR20DET try Venus Auto
www.venus-auto.com
Troy