The spacer actually goes below the engine bracket, resting between the bracket and the top of the engine mount. When the bolt is in place it tightens directly down on the bracket hole shown in the cutaway pic.
There's a similar spacer (unbroken) on the other side. The prev. owner mentioned that he had the engine mounts replaced, so I guess it's possible that someone fashioned the spacer assembly themselves. Sure looks like stock though.
Does anyone know if this is the case? This is the 4.5 engine.