Hello,
You will likely have to go with a seperate source for the harness to run a crated 6.1. You should check the LX Forums for great info and connections. If you don't mind getting a good low mileage 6.1, I would check out Cleveland Pick-A-Part. They dismantle lots of SRT LXs and usually sell the engine/tranny/harnesses as a set. This would likely save you loads over a 'component' set-up.
Good luck!
Paul