ahh this looks familiar. i really wanted an LS1 too, but it really isnt that neccessary.
Many guys bore and stroke the 4.0 and keep everything the same, some guys change out axles, and mix and match all over. you may wanna check out my thread, a lot of guys weighed in on my decision, and i finally came up with my plan. also you may look deeply into novak-adapt's website, as they have just about everything you need to know for any GM (and most other) swaps.
believe it or not my economical MPG came out best with a 5.3, 4 spd, and 373 gears, but to each his own, check mine out here.
my final setup is on the last page, but theres a lot of good info in there