Mileswinger,
I run a wire directly to my alternator from the battery + and -.
Then I have a wire that goes to my frame. There's usually a threaded hole 3/8 bolt (if I recall) to attach your chassis ground wire. You'll need 4 feet if grounding directly from the battery.
Just curious, when you say your engine is disconnected, you mean the transmission? I ask because you should have a wire that goes from the battery to the heads. This is an important connection and you need to make sure you have a good ground (Clean threads and sand paint off where the connection will be made.