Need to make a decision fast 5.7/6.1/340

What needs to be done to the fuel system to run the efi? My plan is to put in stock (maybe a cam) at first then build up. When you buy a megasquirt or holley hp does that replace the stock harness and computer or do i still need the stock harness and computer. I guess im basically looking for a complete parts list that i will need to complete the swap. Thanks for all your input guys