You most definitely will need the engine portion of the harness as well as a PCM. I would start searching for 5.0 wrecks, I'm sure sensor connections will be different. If the swap is done with all stock pieces, it should be indiscernible. You will however cause some Tech some day to scratch his head when he runs your VIN! In a year or so I'm looking for a 3.7L Premium for wifey, she loves her autos. She has driven the BOSS but hated the stick. She had an '01 BULLITT GT but never drove it due to the stick.
Definitely drop your motor from underneath, I did a '98 Z-28 Camaro in 2 hrs with a buddy, unconventional drop method but it worked well.
Yes, I'm a VA hillbilly!