There are so many details with the LS swap. Just converting the fuel system to 60# for EFI is going to be $350 for in-tank, return-less, mostly prefabricated unit. I bought probably $150 of incidental wiring stuff like butt-connectors, crimpers, shrink tubing, terminal blocks, grounding wires etc. Hoses might be $100 as you have to cobble stuff together to fit. Do you really want to use the old knock, MAP, IAT, MAF, cam, and crank sensors? That'll be $150 in new sensors (I reused the MAF). You'll need to cobble together a cold air intake for at least $150. You'll want to know that you have oil pressure, right? That'll prolly be $50 for a simple trouble light that illuminates below 15#. If you use truck accessory bracket, the pinch point is interference with power steering pulley and the steering box; the Holley mounts will make it clear and put the bell housing where it should be. I would not buy the entire Holley kit; the transmission crossmember for 4l60/80e sucks, the "Hooker Blackheart" exhaust manifolds are good, but the exhaust kit from flange-aft sucks... then you are going to lose the speedometer unless you use an older transmission (TH350). I don't think there are any factory exhaust manifolds that fit both the driver and passenger side as a pair; I've heard the trailblazer SS manifold works on one side, not the other. As was mentioned, you need to change the oil pan; I'd use one of the chinesium knock-offs of the Holley 302 series. You'll need the LS1 F-body oil dipstick and you'll have to bend one or buy a Lokar flexible trans dipstick.
I saw electronic pedal brackets for sale at PSIconversion that could make the drive-by-cable to drive-by-wire conversion simple (haven't verified). I used 1998-2004 vintage ECU that allowed me to use drive by cable throttle body. I got an expert to explain to me that not possible to convert Gen4 to drive-by-cable without a bunch of adapters that make it Gen3; IOW can't use VVT on Gen4 with drive-by-cable.