an '02 will be an LQ4 and it is an LS engine, that is one of the most common engine setups out there, that engine is simpler than the newer ones that have the cam phasing (they started around '07 through current, few iterations here and there with MAP sensor changes and E85 injectors in '09 I believe). The 6.0L is a good reliable engine, that's why it is still being made, apparently it's the biggest gas engine you can get in a 2500 or 3500 truck now after they nixed the 8.1L, you can get a direct injected 6.2L (at least 50 more horsepower) in the 1500 but apparently it isn't heavy duty enough for the bigger trucks...
As for a stand alone harness, that shouldn't be too hard to come by, I don't know much about the automotive side of things though as I'm in the Marine side of things... I'm more familiar with the newer engines and what it takes to get them going, we don't have any parts left over from those engines otherwise I would say to ask work tomorrow (although a harness from us is $500+ most likely...)