There has been a couple successful GM LSx swaps. The hard part is dealing with the CANBUS system for the OEM gauges in the RX8, but otherwise the swap can be done. I don't know what all is involved otherwise, but it only adds about 140lbs to the front-middle of the car. Fortunately the RX8s front tires are far enough forward that it only affects the balance by 1-2% roughly of fore/aft weight distribution.