The truck side harness end for both LB7 and LLY are physically the same, they'll plug in under the main fuse box in the engine compartment on top of the inner fender (driver side). So yes, the LLY harness will plug into your trucks fuse box, along with a few other connectors, all of them will plug into the corresponding original connectors under the fuse box. Your LB7 computers will not work with the LLY.
So just to be clear, you will need the LLY motor, ECM/FICM, engine harness (should come with the motor and be attached to it), LLY truck side harness and LLY nsbu.