I built an LSX S13 Coupe for a friend a couple years back... We used a junk yard 5.3 from a truck, changed the intake manifold over to a Camaro/Corvette style intake manifold and put 98-02 Camaro front drive accessories on the car as well. For mounting, headers etc we used all Sikky stuff (
www.sikky.com). To this day everything has held up well.
Sikky sells a complete turnkey drop in LSX kit for $3250 which saves a lot of headaches but is pretty pricey I personally don't mind spending money to have stuff done right but I understand some would rather do it themselves to save some coin and that's fine too.
I do definitely say the 5.3 would be a fine choice, or even the smaller 4.8. Both make similar power and accept the same modifications just as well. A simple heads and cam change on both can net you close to 400whp without any issues.