to put any LSx engine + trans into a thirdgen you will need swap motor mounts, the complete LSx computer and wiring harness, and either an exhaust fabricated off of the stock manifolds or swap headers.
the transmission will actually mount in the same spot and you can retain your stock driveshaft/suspension parts.
you will also want to upgrade yoru fuel pump. jsut grab a walbro 255lph replacement pump and drop it in place of the stocker.
the only other fuel system modification needed is to adapt the fuel lines, which is no big deal.
there are kits available, swap motor mounts, swap headerss, and modified wiring harnesses out there from companies like speartech, hawks parts, spohn, and i think even year one carries some of the swap stuff.
if you want to know mroe in detail, visit the hybrid and conversion forum on
www.LS1tech.com there are a bunch of people there that have done the swap, it is not realy difficult at all.