To clarify further - will both sierra ECU's swap with both looms? Is any ECU particually better, or cheaper to modify / get more power from than another?
And are both / neither looms integral with the main sierra wiring loom - ie will the loom come with a load of redundant wires, or will it be just the Engine loom?
you can put a L8 ecu into a L1 or L6 loom but you will also need to change the Throttle Position Sensor.
the engine loom is separate and just connected to the main loom with a multiplug with 5 or 6 wires for power, temp gauge, oil pressure light and stuff. it's dead easy to use in another vehicle.