I would really check your driveline angle in the mock up stage, if it is like the old Keisler perfect fit deal they supplied a rear cross member that lowered the rear trans mount by about 1.5 inches to have the A41 clear the tunnel. Which in my case caused a vibration issue, hence the reason I have a 855 in my car, which has been awesome since Aug 2013 and is getting close to 10000 miles on it.
Just Sayin