Just some Questions needing answers

[Cthibo500]

Looking into doing a LSx swap. wondering if anyone can point me in the right direction and info.
Looking to build a MILD motor. i'm wanting an all aluminum 5.3 so from what i read its a L33? they're available in 2005+ models? I dont mind the DBW because I want to be able to put the pedal in whatever position I want for heel toe downshifts.
For mods I'm shooting for 400HP and I want it to freely spin 6K. probably have the heads polished and a mild cam. Would a different intake be worth it? I dont like the original 5.3 looks like ****. LS1 vs LS? which one is worth the money. Also, would a bigger throttle body thats DBW be worth it?
Theres no A.C so I'm not worried about that.
as Far as ECU's and Wiring. should i shoot for Factory Wiring or get an aftermarket kit for it. if so anyone have any good locations for them? the ECU will be factory. I live in an area that does not have much for tuning shops so that is kind of out of the question. unless I sent it out.
Transmission WILL BE a TKO500. Want some OK mpg out of it. also thinking rear gears as a 3.73 gear ratio.

Truck is a 1981 C10 Stepside. weighs aprox 4000lbs.

any tips and pointers would be greatly appreciated