Here is a photo that shows the clearance. It is about 3.125 inches between the back of the block and the frame. I have a short 930 tranny, so I could not move the motor any further forward that what you see here. I would be curious to see the clearance that other LS powered 911's have.
The RH motor mounts allow a lot of movement front to back to accommodate different tranny/chassis combos.
