The best way to do the exhaust system would be from the manifolds rearward, and to put a cross over pipe into the system before it enters the mufflers. I don't see anything wrong with going with a 2 inch system, and it will help the engine to breath a little bit better. I wouldn't go with anything larger than the 2" system, since you need to have a small amount of back pressure. I would also have the pipes exit just behind the rear wheels, so you don't pick up any exhaust fumes in the patient compartment. I found this to be a problem with my 1963 Chrysler, and have advised Nick that he should have this corrected before he puts anyone in the rear. After my experience of driving home from Flint in 2009, and becoming drowsy, and not knowing why, I believe that it would be wise and prudent to have a carbon monoxide detector in the rear of all our professional cars, with the exception of a flower car. You can never be too safe.