You can see the off-set of the engine here. If you look at the left side of the picture you'll notice that I'm not using the "Slot" that the factory mount did. There was another hole further back in the factory mount that I used.
Since I'm using old arms that are rusty and the rubber is pretty soft from 200,000 of flexing I wanted to stay as far away from the rubber in the bushing as I could. If I was using a new arm I'd have likley used the factory mounting holes on the frame mounts.