Ly5 5.3 carburated
You'll need an MSD 6012 box for the 58x crank wheel.
A microsquirt plug and play kit that is a stand-alone with a complete harness ready to go is only $800 or so (cheaper depending on where you get it). About the same price as a new intake/msd and an old carb, and it will work with the factory intake, injectors, etc.

