For all Holley ECU's, the power and ground should be connected directly to the battery. In fact, anything ecu or ignition related should be connected directly to the battery both positive and negative. Why? The battery acts as a capacitor to soak up voltage fluctuations and such. Same thing if you have an electric fan.
As for ground, the battery should be connected to a good solid section of the chassis without paint. The engine and alternator grounds should also run to the same spot on the chassis as well.
Gotta remember, with EFI, all the old rules of wiring in these cars goes out the window. EFI is very sensitive to interference and can be a nightmare to fix if your wiring isn't 100%.
Ask me how I know all this.
-Shannon