Gordon it's my understanding (I admit I don't have hard #s to support) that the T56 trans is heavier than the Mazda trans. In other words, when considering all the turbos, etc. up front and high on the 13B, the LSx/T56 combination actually results in a lower polar moment for the entire car, even though F/R weight balance is essentially unchanged.

Oh, and you might be surprised at how low the LSx actually sits in the car. Ground clearance can be a Major Issue with these swaps. The bottom of my oil pan has a nice grooved texture, specially applied by a stationary asphalt grinding surface... :)