Without sounding redundant because Fred made some good suggestions already...The driveline tunnel centerline is set up for the factory 1 3/16" offset. Verify the position of the pinion yoke and align the eng./trans. from there. If for any number of reasons the rear isn't at that position and you slam (lower) the car and/or run a large diameter driveshaft (3.5+inch) you will experience interference with the tunnel. With the big power you are sure to be making (It's in your nature.) spend the extra time properly aligning the driveline accurately.